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<!DOCTYPE html>
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<title>Iterative Programming | Practical Data Science</title>
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<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#part-2-programming-basics"><i class="fa fa-check"></i>Part 2: Programming Basics</a></li>
<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#part-3-modeling"><i class="fa fa-check"></i>Part 3: Modeling</a></li>
<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#part-4-visualization"><i class="fa fa-check"></i>Part 4: Visualization</a></li>
<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#part-5-presentation"><i class="fa fa-check"></i>Part 5: Presentation</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#workshops"><i class="fa fa-check"></i>Workshops</a></li>
<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#other"><i class="fa fa-check"></i>Other</a>
<ul>
<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#python-notebooks"><i class="fa fa-check"></i>Python notebooks</a></li>
<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#other-r-packages"><i class="fa fa-check"></i>Other R packages</a></li>
<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#history"><i class="fa fa-check"></i>History</a></li>
<li class="chapter" data-level="" data-path="intro.html"><a href="intro.html#current-efforts"><i class="fa fa-check"></i>Current Efforts</a></li>
</ul></li>
</ul></li>
<li class="part"><span><b>Part I: Information Processing</b></span></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html"><i class="fa fa-check"></i>Data Structures</a>
<ul>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#vectors"><i class="fa fa-check"></i>Vectors</a>
<ul>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#character-strings"><i class="fa fa-check"></i>Character strings</a></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#factors"><i class="fa fa-check"></i>Factors</a></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#logicals"><i class="fa fa-check"></i>Logicals</a></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#numeric-and-integer"><i class="fa fa-check"></i>Numeric and integer</a></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#dates"><i class="fa fa-check"></i>Dates</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#matrices"><i class="fa fa-check"></i>Matrices</a>
<ul>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#creating-a-matrix"><i class="fa fa-check"></i>Creating a matrix</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#lists"><i class="fa fa-check"></i>Lists</a></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#data-frames"><i class="fa fa-check"></i>Data Frames</a>
<ul>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#creating-a-data-frame"><i class="fa fa-check"></i>Creating a data frame</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#data-structure-exercises"><i class="fa fa-check"></i>Data Structure Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#exercise-1"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#exercise-2"><i class="fa fa-check"></i>Exercise 2</a></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#thinking-exercises"><i class="fa fa-check"></i>Thinking Exercises</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="data_structures.html"><a href="data_structures.html#python-data-structures-notebook"><i class="fa fa-check"></i>Python Data Structures Notebook</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html"><i class="fa fa-check"></i>Input/Output</a>
<ul>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#better-faster-approaches"><i class="fa fa-check"></i>Better & Faster Approaches</a></li>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#r-specific-data"><i class="fa fa-check"></i>R-specific Data</a>
<ul>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#r-datasets"><i class="fa fa-check"></i>R Datasets</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#other-types-of-data"><i class="fa fa-check"></i>Other Types of Data</a></li>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#on-the-horizon"><i class="fa fa-check"></i>On the Horizon</a></li>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#big-data"><i class="fa fa-check"></i>Big Data</a></li>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#io-exercises"><i class="fa fa-check"></i>I/O Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#exercise-1-1"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#thinking-exercises-1"><i class="fa fa-check"></i>Thinking Exercises</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="io.html"><a href="io.html#python-io-notebook"><i class="fa fa-check"></i>Python I/O Notebook</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html"><i class="fa fa-check"></i>Indexing</a>
<ul>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#slicing-vectors"><i class="fa fa-check"></i>Slicing Vectors</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#slicing-matricesdata.frames"><i class="fa fa-check"></i>Slicing Matrices/data.frames</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#label-based-indexing"><i class="fa fa-check"></i>Label-based Indexing</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#position-based-indexing"><i class="fa fa-check"></i>Position-based Indexing</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#mixed-indexing"><i class="fa fa-check"></i>Mixed Indexing</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#non-contiguous"><i class="fa fa-check"></i>Non-contiguous</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#boolean"><i class="fa fa-check"></i>Boolean</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#listdata.frame-extraction"><i class="fa fa-check"></i>List/data.frame Extraction</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#indexing-exercises"><i class="fa fa-check"></i>Indexing Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#exercise-1-2"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#exercise-2-1"><i class="fa fa-check"></i>Exercise 2</a></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#exercise-3"><i class="fa fa-check"></i>Exercise 3</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="indexing.html"><a href="indexing.html#python-indexing-notebook"><i class="fa fa-check"></i>Python Indexing Notebook</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="pipes.html"><a href="pipes.html"><i class="fa fa-check"></i>Pipes</a>
<ul>
<li class="chapter" data-level="" data-path="pipes.html"><a href="pipes.html#using-variables-as-they-are-created"><i class="fa fa-check"></i>Using Variables as They are Created</a></li>
<li class="chapter" data-level="" data-path="pipes.html"><a href="pipes.html#pipes-for-visualization-more-later"><i class="fa fa-check"></i>Pipes for Visualization (more later)</a></li>
<li class="chapter" data-level="" data-path="pipes.html"><a href="pipes.html#the-dot"><i class="fa fa-check"></i>The Dot</a></li>
<li class="chapter" data-level="" data-path="pipes.html"><a href="pipes.html#flexibility"><i class="fa fa-check"></i>Flexibility</a></li>
<li class="chapter" data-level="" data-path="pipes.html"><a href="pipes.html#pipes-summary"><i class="fa fa-check"></i>Pipes Summary</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html"><i class="fa fa-check"></i>Tidyverse</a>
<ul>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#what-is-the-tidyverse"><i class="fa fa-check"></i>What is the Tidyverse?</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#what-is-tidy"><i class="fa fa-check"></i>What is Tidy?</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#dplyr"><i class="fa fa-check"></i>dplyr</a>
<ul>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#an-example"><i class="fa fa-check"></i>An example</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#running-example"><i class="fa fa-check"></i>Running Example</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#selecting-columns"><i class="fa fa-check"></i>Selecting Columns</a>
<ul>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#helper-functions"><i class="fa fa-check"></i>Helper functions</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#filtering-rows"><i class="fa fa-check"></i>Filtering Rows</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#generating-new-data"><i class="fa fa-check"></i>Generating New Data</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#grouping-and-summarizing-data"><i class="fa fa-check"></i>Grouping and Summarizing Data</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#renaming-columns"><i class="fa fa-check"></i>Renaming Columns</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#merging-data"><i class="fa fa-check"></i>Merging Data</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#pivoting-axes"><i class="fa fa-check"></i>Pivoting axes</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#more-tidyverse"><i class="fa fa-check"></i>More Tidyverse</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#personal-opinion"><i class="fa fa-check"></i>Personal Opinion</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#tidyverse-exercises"><i class="fa fa-check"></i>Tidyverse Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#exercise-0"><i class="fa fa-check"></i>Exercise 0</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#exercise-1-3"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#exercise-2-2"><i class="fa fa-check"></i>Exercise 2</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#exercise-3-1"><i class="fa fa-check"></i>Exercise 3</a></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#exercise-4"><i class="fa fa-check"></i>Exercise 4</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="tidyverse.html"><a href="tidyverse.html#python-pandas-notebook"><i class="fa fa-check"></i>Python Pandas Notebook</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html"><i class="fa fa-check"></i>data.table</a>
<ul>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#data.table-basics"><i class="fa fa-check"></i>data.table Basics</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#grouped-operations"><i class="fa fa-check"></i>Grouped Operations</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#faster"><i class="fa fa-check"></i>Faster!</a>
<ul>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#joins"><i class="fa fa-check"></i>Joins</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#group-by"><i class="fa fa-check"></i>Group by</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#string-matching"><i class="fa fa-check"></i>String matching</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#reading-files"><i class="fa fa-check"></i>Reading files</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#more-speed"><i class="fa fa-check"></i>More speed</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#pipe-with-data.table"><i class="fa fa-check"></i>Pipe with data.table</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#data.table-summary"><i class="fa fa-check"></i>data.table Summary</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#faster-dplyr-alternatives"><i class="fa fa-check"></i>Faster dplyr Alternatives</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#data.table-exercises"><i class="fa fa-check"></i>data.table Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#exercise-0-1"><i class="fa fa-check"></i>Exercise 0</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#exercise-1-4"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="data_table.html"><a href="data_table.html#exercise-2-3"><i class="fa fa-check"></i>Exercise 2</a></li>
</ul></li>
</ul></li>
<li class="part"><span><b>Part II: Programming</b></span></li>
<li class="chapter" data-level="" data-path="programming.html"><a href="programming.html"><i class="fa fa-check"></i>Programming Basics</a>
<ul>
<li class="chapter" data-level="" data-path="programming.html"><a href="programming.html#r-objects"><i class="fa fa-check"></i>R Objects</a>
<ul>
<li class="chapter" data-level="" data-path="programming.html"><a href="programming.html#object-inspection-exploration"><i class="fa fa-check"></i>Object Inspection & Exploration</a></li>
<li class="chapter" data-level="" data-path="programming.html"><a href="programming.html#methods"><i class="fa fa-check"></i>Methods</a></li>
<li class="chapter" data-level="" data-path="programming.html"><a href="programming.html#s4-classes"><i class="fa fa-check"></i>S4 classes</a></li>
<li class="chapter" data-level="" data-path="programming.html"><a href="programming.html#others"><i class="fa fa-check"></i>Others</a></li>
<li class="chapter" data-level="" data-path="programming.html"><a href="programming.html#inspecting-functions"><i class="fa fa-check"></i>Inspecting Functions</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="programming.html"><a href="programming.html#documentation"><i class="fa fa-check"></i>Documentation</a></li>
<li class="chapter" data-level="" data-path="programming.html"><a href="programming.html#objects-exercises"><i class="fa fa-check"></i>Objects Exercises</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html"><i class="fa fa-check"></i>Iterative Programming</a>
<ul>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#for-loops"><i class="fa fa-check"></i>For Loops</a>
<ul>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#a-slight-speed-gain"><i class="fa fa-check"></i>A slight speed gain</a></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#while-alternative"><i class="fa fa-check"></i>While alternative</a></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#loops-summary"><i class="fa fa-check"></i>Loops summary</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#implicit-loops"><i class="fa fa-check"></i>Implicit Loops</a>
<ul>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#apply-family"><i class="fa fa-check"></i>apply family</a></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#apply-functions"><i class="fa fa-check"></i>Apply functions</a></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#purrr"><i class="fa fa-check"></i>purrr</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#looping-with-lists"><i class="fa fa-check"></i>Looping with Lists</a></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#iterative-programming-exercises"><i class="fa fa-check"></i>Iterative Programming Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#exercise-1-5"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#exercise-2-4"><i class="fa fa-check"></i>Exercise 2</a></li>
<li class="chapter" data-level="" data-path="iterative.html"><a href="iterative.html#exercise-3-2"><i class="fa fa-check"></i>Exercise 3</a></li>
</ul></li>
</ul></li>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html"><i class="fa fa-check"></i>Writing Functions</a>
<ul>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html#a-starting-point"><i class="fa fa-check"></i>A Starting Point</a></li>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html#dry"><i class="fa fa-check"></i>DRY</a></li>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html#conditionals"><i class="fa fa-check"></i>Conditionals</a></li>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html#anonymous-functions"><i class="fa fa-check"></i>Anonymous functions</a></li>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html#writing-functions-exercises"><i class="fa fa-check"></i>Writing Functions Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html#excercise-1"><i class="fa fa-check"></i>Excercise 1</a></li>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html#excercise-1b"><i class="fa fa-check"></i>Excercise 1b</a></li>
<li class="chapter" data-level="" data-path="functions.html"><a href="functions.html#exercise-2-5"><i class="fa fa-check"></i>Exercise 2</a></li>
</ul></li>
</ul></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html"><i class="fa fa-check"></i>More Programming</a>
<ul>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#code-style"><i class="fa fa-check"></i>Code Style</a>
<ul>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#why-does-your-code-exist"><i class="fa fa-check"></i>Why does your code exist?</a></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#assignment"><i class="fa fa-check"></i>Assignment</a></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#code-length"><i class="fa fa-check"></i>Code length</a></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#spacing"><i class="fa fa-check"></i>Spacing</a></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#naming-things"><i class="fa fa-check"></i>Naming things</a></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#other-1"><i class="fa fa-check"></i>Other</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#vectorization"><i class="fa fa-check"></i>Vectorization</a>
<ul>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#boolean-indexing"><i class="fa fa-check"></i>Boolean indexing</a></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#vectorized-operations"><i class="fa fa-check"></i>Vectorized operations</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#regular-expressions"><i class="fa fa-check"></i>Regular Expressions</a>
<ul>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#typical-uses"><i class="fa fa-check"></i>Typical uses</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#code-style-exercises"><i class="fa fa-check"></i>Code Style Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#exercise-1-6"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#exercise-2-6"><i class="fa fa-check"></i>Exercise 2</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#vectorization-exercises"><i class="fa fa-check"></i>Vectorization Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#exercise-1-7"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#exercise-2-7"><i class="fa fa-check"></i>Exercise 2</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#regex-exercises"><i class="fa fa-check"></i>Regex Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="more.html"><a href="more.html#exercise-1-8"><i class="fa fa-check"></i>Exercise 1</a></li>
</ul></li>
</ul></li>
<li class="part"><span><b>Part III: Modeling</b></span></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html"><i class="fa fa-check"></i>Model Exploration</a>
<ul>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#model-taxonomy"><i class="fa fa-check"></i>Model Taxonomy</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#linear-models"><i class="fa fa-check"></i>Linear models</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#estimation"><i class="fa fa-check"></i>Estimation</a>
<ul>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#minimizing-and-maximizing"><i class="fa fa-check"></i>Minimizing and maximizing</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#optimization"><i class="fa fa-check"></i>Optimization</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#fitting-models"><i class="fa fa-check"></i>Fitting Models</a>
<ul>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#using-matrices"><i class="fa fa-check"></i>Using matrices</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#summarizing-models"><i class="fa fa-check"></i>Summarizing Models</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#variable-transformations"><i class="fa fa-check"></i>Variable Transformations</a>
<ul>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#numeric-variables"><i class="fa fa-check"></i>Numeric variables</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#categorical-variables"><i class="fa fa-check"></i>Categorical variables</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#scales-indices-and-dimension-reduction"><i class="fa fa-check"></i>Scales, indices, and dimension reduction</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#dont-discretize"><i class="fa fa-check"></i>Don’t discretize</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#variable-importance"><i class="fa fa-check"></i>Variable Importance</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#extracting-output"><i class="fa fa-check"></i>Extracting Output</a>
<ul>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#package-support"><i class="fa fa-check"></i>Package support</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#visualization"><i class="fa fa-check"></i>Visualization</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#extensions-to-the-standard-linear-model"><i class="fa fa-check"></i>Extensions to the Standard Linear Model</a>
<ul>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#different-types-of-targets"><i class="fa fa-check"></i>Different types of targets</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#correlated-data"><i class="fa fa-check"></i>Correlated data</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#other-extensions"><i class="fa fa-check"></i>Other extensions</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#model-exploration-summary"><i class="fa fa-check"></i>Model Exploration Summary</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#model-exploration-exercises"><i class="fa fa-check"></i>Model Exploration Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#exercise-1-9"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#exercise-2-8"><i class="fa fa-check"></i>Exercise 2</a></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#exercise-3-3"><i class="fa fa-check"></i>Exercise 3</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="models.html"><a href="models.html#python-model-exploration-notebook"><i class="fa fa-check"></i>Python Model Exploration Notebook</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html"><i class="fa fa-check"></i>Model Criticism</a>
<ul>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#model-fit"><i class="fa fa-check"></i>Model Fit</a>
<ul>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#standard-linear-model"><i class="fa fa-check"></i>Standard linear model</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#beyond-ols"><i class="fa fa-check"></i>Beyond OLS</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#classification"><i class="fa fa-check"></i>Classification</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#model-assumptions"><i class="fa fa-check"></i>Model Assumptions</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#predictive-performance"><i class="fa fa-check"></i>Predictive Performance</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#model-comparison"><i class="fa fa-check"></i>Model Comparison</a>
<ul>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#example-additional-covariates"><i class="fa fa-check"></i>Example: Additional covariates</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#example-interactions"><i class="fa fa-check"></i>Example: Interactions</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#example-additive-models"><i class="fa fa-check"></i>Example: Additive models</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#model-averaging"><i class="fa fa-check"></i>Model Averaging</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#model-criticism-summary"><i class="fa fa-check"></i>Model Criticism Summary</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#model-criticism-exercises"><i class="fa fa-check"></i>Model Criticism Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#exercise-0-2"><i class="fa fa-check"></i>Exercise 0</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#exercise-1-10"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#exercise-2-9"><i class="fa fa-check"></i>Exercise 2</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="model_criticism.html"><a href="model_criticism.html#python-model-criticism-notebook"><i class="fa fa-check"></i>Python Model Criticism Notebook</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html"><i class="fa fa-check"></i>Machine Learning</a>
<ul>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#concepts"><i class="fa fa-check"></i>Concepts</a>
<ul>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#loss"><i class="fa fa-check"></i>Loss</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#bias-variance-tradeoff"><i class="fa fa-check"></i>Bias-variance tradeoff</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#regularization"><i class="fa fa-check"></i>Regularization</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#cross-validation"><i class="fa fa-check"></i>Cross-validation</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#optimization-1"><i class="fa fa-check"></i>Optimization</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#tuning-parameters"><i class="fa fa-check"></i>Tuning parameters</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#techniques"><i class="fa fa-check"></i>Techniques</a>
<ul>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#regularized-regression"><i class="fa fa-check"></i>Regularized regression</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#random-forests"><i class="fa fa-check"></i>Random forests</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#neural-networks"><i class="fa fa-check"></i>Neural networks</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#interpreting-the-black-box"><i class="fa fa-check"></i>Interpreting the Black Box</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#machine-learning-summary"><i class="fa fa-check"></i>Machine Learning Summary</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#machine-learning-exercises"><i class="fa fa-check"></i>Machine Learning Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#exercise-1-11"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#exercise-2-10"><i class="fa fa-check"></i>Exercise 2</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="ml.html"><a href="ml.html#python-machine-learning-notebook"><i class="fa fa-check"></i>Python Machine Learning Notebook</a></li>
</ul></li>
<li class="part"><span><b>Part IV: Visualization</b></span></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html"><i class="fa fa-check"></i>ggplot2</a>
<ul>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#layers"><i class="fa fa-check"></i>Layers</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#piping"><i class="fa fa-check"></i>Piping</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#aesthetics"><i class="fa fa-check"></i>Aesthetics</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#geoms"><i class="fa fa-check"></i>Geoms</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#examples"><i class="fa fa-check"></i>Examples</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#stats"><i class="fa fa-check"></i>Stats</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#scales"><i class="fa fa-check"></i>Scales</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#facets"><i class="fa fa-check"></i>Facets</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#multiple-plots"><i class="fa fa-check"></i>Multiple plots</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#fine-control"><i class="fa fa-check"></i>Fine control</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#themes"><i class="fa fa-check"></i>Themes</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#extensions"><i class="fa fa-check"></i>Extensions</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#ggplot2-summary"><i class="fa fa-check"></i>ggplot2 Summary</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#ggplot2-exercises"><i class="fa fa-check"></i>ggplot2 Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#exercise-0-3"><i class="fa fa-check"></i>Exercise 0</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#exercise-1-12"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#exercise-2-11"><i class="fa fa-check"></i>Exercise 2</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="ggplot2.html"><a href="ggplot2.html#python-plotnine-notebook"><i class="fa fa-check"></i>Python Plotnine Notebook</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html"><i class="fa fa-check"></i>Interactive Visualization</a>
<ul>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#packages"><i class="fa fa-check"></i>Packages</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#piping-for-visualization"><i class="fa fa-check"></i>Piping for Visualization</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#htmlwidgets"><i class="fa fa-check"></i>htmlwidgets</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#plotly"><i class="fa fa-check"></i>Plotly</a>
<ul>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#modes"><i class="fa fa-check"></i>Modes</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#ggplotly"><i class="fa fa-check"></i>ggplotly</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#highcharter"><i class="fa fa-check"></i>Highcharter</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#graph-networks"><i class="fa fa-check"></i>Graph networks</a>
<ul>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#visnetwork"><i class="fa fa-check"></i>visNetwork</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#sigmajs"><i class="fa fa-check"></i>sigmajs</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#plotly-1"><i class="fa fa-check"></i>Plotly</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#leaflet"><i class="fa fa-check"></i>leaflet</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#dt"><i class="fa fa-check"></i>DT</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#shiny"><i class="fa fa-check"></i>Shiny</a>
<ul>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#dash"><i class="fa fa-check"></i>Dash</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#interactive-and-visual-data-exploration"><i class="fa fa-check"></i>Interactive and Visual Data Exploration</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#interactive-visualization-exercises"><i class="fa fa-check"></i>Interactive Visualization Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#exercise-0-4"><i class="fa fa-check"></i>Exercise 0</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#exercise-1-13"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#exercise-2-12"><i class="fa fa-check"></i>Exercise 2</a></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#exercise-3-4"><i class="fa fa-check"></i>Exercise 3</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="interactive.html"><a href="interactive.html#python-interactive-visualization-notebook"><i class="fa fa-check"></i>Python Interactive Visualization Notebook</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html"><i class="fa fa-check"></i>Thinking Visually</a>
<ul>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#information"><i class="fa fa-check"></i>Information</a>
<ul>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#your-audience-isnt-dumb"><i class="fa fa-check"></i>Your audience isn’t dumb</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#clarity-is-key"><i class="fa fa-check"></i>Clarity is key</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#avoid-clutter"><i class="fa fa-check"></i>Avoid clutter</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#color-isnt-optional"><i class="fa fa-check"></i>Color isn’t optional</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#think-interactively"><i class="fa fa-check"></i>Think interactively</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#color"><i class="fa fa-check"></i>Color</a>
<ul>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#viridis"><i class="fa fa-check"></i>Viridis</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#scientific-colors"><i class="fa fa-check"></i>Scientific colors</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#rcolorbrewer"><i class="fa fa-check"></i>RColorBrewer</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#contrast"><i class="fa fa-check"></i>Contrast</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#scaling-size"><i class="fa fa-check"></i>Scaling Size</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#transparency"><i class="fa fa-check"></i>Transparency</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#accessibility"><i class="fa fa-check"></i>Accessibility</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#file-types"><i class="fa fa-check"></i>File Types</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#summary-of-thinking-visually"><i class="fa fa-check"></i>Summary of Thinking Visually</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#a-casual-list-of-things-to-avoid"><i class="fa fa-check"></i>A casual list of things to avoid</a>
<ul>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#pie"><i class="fa fa-check"></i>Pie</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#histograms"><i class="fa fa-check"></i>Histograms</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#using-3d-without-adding-any-communicative-value"><i class="fa fa-check"></i>Using 3D without adding any communicative value</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#using-too-many-colors"><i class="fa fa-check"></i>Using too many colors</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#using-valenced-colors-when-data-isnt-applicable"><i class="fa fa-check"></i>Using valenced colors when data isn’t applicable</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#showing-maps-that-just-display-population"><i class="fa fa-check"></i>Showing maps that just display population</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#biplots"><i class="fa fa-check"></i>Biplots</a></li>
</ul></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#thinking-visually-exercises"><i class="fa fa-check"></i>Thinking Visually Exercises</a>
<ul>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#exercise-1-14"><i class="fa fa-check"></i>Exercise 1</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#exercise-2-13"><i class="fa fa-check"></i>Exercise 2</a></li>
<li class="chapter" data-level="" data-path="thinking_vis.html"><a href="thinking_vis.html#thinking-exercises-2"><i class="fa fa-check"></i>Thinking exercises</a></li>
</ul></li>
</ul></li>
<li class="part"><span><b>Part V: Presentation</b></span></li>
<li class="chapter" data-level="" data-path="reproducibility.html"><a href="reproducibility.html"><i class="fa fa-check"></i>Building Better Data-Driven Products</a>
<ul>
<li class="chapter" data-level="" data-path="reproducibility.html"><a href="reproducibility.html#rep-analysis"><i class="fa fa-check"></i>Rep* Analysis</a>
<ul>
<li class="chapter" data-level="" data-path="reproducibility.html"><a href="reproducibility.html#example"><i class="fa fa-check"></i>Example</a></li>
<li class="chapter" data-level="" data-path="reproducibility.html"><a href="reproducibility.html#repeatable"><i class="fa fa-check"></i>Repeatable</a></li>
<li class="chapter" data-level="" data-path="reproducibility.html"><a href="reproducibility.html#reproducible"><i class="fa fa-check"></i>Reproducible</a></li>
<li class="chapter" data-level="" data-path="reproducibility.html"><a href="reproducibility.html#replicable"><i class="fa fa-check"></i>Replicable</a></li>
<li class="chapter" data-level="" data-path="reproducibility.html"><a href="reproducibility.html#summary-of-rep-analysis"><i class="fa fa-check"></i>Summary of rep* analysis</a></li>
</ul></li>
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<i class="fa fa-circle-o-notch fa-spin"></i><a href="./">Practical Data Science</a>
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<section class="normal" id="section-">
<div id="iterative-programming" class="section level1">
<h1>Iterative Programming</h1>
<div style="text-align: center;">
<p><i class="fas fa-sync-alt fa-5x" ></i></p>
</div>
<p><br></p>
<p>Almost everything you do when dealing with data will need to be done again, and again, and again. If you are copy-pasting your way to repetitively do the same thing, you’re not only doing things inefficiently, you’re almost certainly setting yourself up for trouble if anything changes about the data or underlying process.</p>
<p>In order to avoid this, you need to be familiar with basic programming, and a starting point is to use an iterative approach to repetitive problems. Let’s look at the following. Let’s say we want to get the means of some columns in our data set. Do you do something like this?</p>
<div class="sourceCode" id="cb257"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb257-1"><a href="iterative.html#cb257-1"></a>means1 =<span class="st"> </span><span class="kw">mean</span>(df<span class="op">$</span>x)</span>
<span id="cb257-2"><a href="iterative.html#cb257-2"></a>means2 =<span class="st"> </span><span class="kw">mean</span>(df<span class="op">$</span>y)</span>
<span id="cb257-3"><a href="iterative.html#cb257-3"></a>means3 =<span class="st"> </span><span class="kw">mean</span>(df<span class="op">$</span>z)</span>
<span id="cb257-4"><a href="iterative.html#cb257-4"></a>means4 =<span class="st"> </span><span class="kw">mean</span>(df<span class="op">$</span>q)</span></code></pre></div>
<p>Now consider what you have to change if you change a variable name, decide to do a median, or the data object name changes. Any minor change with the data will cause you to have to redo that code, and possibly every line of it.</p>
<div id="for-loops" class="section level2">
<h2>For Loops</h2>
<p>A <span class="emph">for loop</span> will help us get around the problem. The idea is that we want to perform a particular action <em>for</em> every iteration of some sequence. That sequence may be over columns, rows, lines in a text, whatever. Here is a loop.</p>
<div class="sourceCode" id="cb258"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb258-1"><a href="iterative.html#cb258-1"></a><span class="cf">for</span> (column <span class="cf">in</span> <span class="kw">c</span>(<span class="st">'x'</span>,<span class="st">'y'</span>,<span class="st">'z'</span>,<span class="st">'q'</span>)) {</span>
<span id="cb258-2"><a href="iterative.html#cb258-2"></a> <span class="kw">mean</span>(df[[column]])</span>
<span id="cb258-3"><a href="iterative.html#cb258-3"></a>}</span></code></pre></div>
<p>What’s going on here? We’ve created an iterative process in which, <em>for</em> every <em>element</em> in <code>c('x','y','z','q')</code>, we are going to do something. We use the completely arbitrary word <code>column</code> as a placeholder to index which of the four columns we’re dealing with at a given point in the process. On the first iteration, <code>column</code> will equal <code>x</code>, on the second <code>y</code>, and so on. We then take the mean of <code>df[[column]]</code>, which will be <code>df[['x']]</code>, then <code>df[['y']]</code>, etc.</p>
<p>Here is an example with the <span class="pack">nycflights</span> data, which regards flights that departed New York City in 2013. The <span class="objclass">weather</span> data set has columns for things like temperature, humidity, and so forth.</p>
<div class="sourceCode" id="cb259"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb259-1"><a href="iterative.html#cb259-1"></a>weather =<span class="st"> </span>nycflights13<span class="op">::</span>weather</span>
<span id="cb259-2"><a href="iterative.html#cb259-2"></a></span>
<span id="cb259-3"><a href="iterative.html#cb259-3"></a><span class="cf">for</span> (column <span class="cf">in</span> <span class="kw">c</span>(<span class="st">'temp'</span>, <span class="st">'humid'</span>, <span class="st">'wind_speed'</span>, <span class="st">'precip'</span>)) {</span>
<span id="cb259-4"><a href="iterative.html#cb259-4"></a> <span class="kw">print</span>(<span class="kw">mean</span>(weather[[column]], <span class="dt">na.rm =</span> <span class="ot">TRUE</span>))</span>
<span id="cb259-5"><a href="iterative.html#cb259-5"></a>}</span></code></pre></div>
<pre><code>[1] 55.26039
[1] 62.53006
[1] 10.51749
[1] 0.004469079</code></pre>
<p>You can check this for yourself by testing a column or two directly with just <code>mean(df$x)</code>.</p>
<p>Now if the data name changes, the columns we want change, or we want to calculate something else, we usually end up only changing one thing, rather than at least changing one at a minimum, and probably many more things. In addition, the amount of code is the same whether the loop goes over 100 columns or 4.</p>
<p>Let’s do things a little differently.</p>
<div class="sourceCode" id="cb261"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb261-1"><a href="iterative.html#cb261-1"></a>columns =<span class="st"> </span><span class="kw">c</span>(<span class="st">'temp'</span>, <span class="st">'humid'</span>, <span class="st">'wind_speed'</span>, <span class="st">'precip'</span>)</span>
<span id="cb261-2"><a href="iterative.html#cb261-2"></a>nyc_means =<span class="st"> </span><span class="kw">rep</span>(<span class="ot">NA</span>, <span class="kw">length</span>(columns))</span>
<span id="cb261-3"><a href="iterative.html#cb261-3"></a></span>
<span id="cb261-4"><a href="iterative.html#cb261-4"></a><span class="cf">for</span> (i <span class="cf">in</span> <span class="kw">seq_along</span>(columns)) {</span>
<span id="cb261-5"><a href="iterative.html#cb261-5"></a> column =<span class="st"> </span>columns[i]</span>
<span id="cb261-6"><a href="iterative.html#cb261-6"></a> nyc_means[i] =<span class="st"> </span><span class="kw">mean</span>(weather[[column]], <span class="dt">na.rm =</span> <span class="ot">TRUE</span>)</span>
<span id="cb261-7"><a href="iterative.html#cb261-7"></a> </span>
<span id="cb261-8"><a href="iterative.html#cb261-8"></a> <span class="co"># alternative without the initial first step</span></span>
<span id="cb261-9"><a href="iterative.html#cb261-9"></a> <span class="co"># nyc_means[i] = mean(weather[[columns[i]]], na.rm = TRUE) </span></span>
<span id="cb261-10"><a href="iterative.html#cb261-10"></a>}</span>
<span id="cb261-11"><a href="iterative.html#cb261-11"></a></span>
<span id="cb261-12"><a href="iterative.html#cb261-12"></a>nyc_means</span></code></pre></div>
<pre><code>[1] 55.260392127 62.530058972 10.517488384 0.004469079</code></pre>
<p>By creating a <span class="objclass">columns</span> object, if anything changes about the columns we want, that’s the only line in the code that would need to be changed. The <code>i</code> is now a place holder for a number that goes from 1 to the length of <span class="objclass">columns</span> (i.e. 4). We make an empty <span class="objclass">nyc_means</span> object that’s the length of the columns, so that each element will eventually be the mean of the corresponding column.</p>
<p>In the following I remove precipitation and add visibility and air pressure.</p>
<div class="sourceCode" id="cb263"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb263-1"><a href="iterative.html#cb263-1"></a>columns =<span class="st"> </span><span class="kw">c</span>(<span class="st">'temp'</span>, <span class="st">'humid'</span>, <span class="st">'wind_speed'</span>, <span class="st">'visib'</span>, <span class="st">'pressure'</span>)</span>
<span id="cb263-2"><a href="iterative.html#cb263-2"></a>nyc_means =<span class="st"> </span><span class="kw">rep</span>(<span class="ot">NA</span>, <span class="kw">length</span>(columns))</span>
<span id="cb263-3"><a href="iterative.html#cb263-3"></a></span>
<span id="cb263-4"><a href="iterative.html#cb263-4"></a><span class="cf">for</span> (i <span class="cf">in</span> <span class="kw">seq_along</span>(columns)) {</span>
<span id="cb263-5"><a href="iterative.html#cb263-5"></a> nyc_means[i] =<span class="st"> </span><span class="kw">mean</span>(weather[[columns[i]]], <span class="dt">na.rm =</span> <span class="ot">TRUE</span>)</span>
<span id="cb263-6"><a href="iterative.html#cb263-6"></a>}</span>
<span id="cb263-7"><a href="iterative.html#cb263-7"></a></span>
<span id="cb263-8"><a href="iterative.html#cb263-8"></a>nyc_means <span class="op">%>%</span><span class="st"> </span><span class="kw">round</span>(<span class="dv">2</span>)</span></code></pre></div>
<pre><code>[1] 55.26 62.53 10.52 9.26 1017.90</code></pre>
<p>Had we been copy-pasting, this would require deleting or commenting out a line in our code, pasting two more, and changing each one after pasting to represent the new columns. That’s tedious, and not a fun way to code.</p>
<div id="a-slight-speed-gain" class="section level3">
<h3>A slight speed gain</h3>
<p>Note that you do not have to create an empty object like we did. The following works also.</p>
<div class="sourceCode" id="cb265"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb265-1"><a href="iterative.html#cb265-1"></a>columns =<span class="st"> </span><span class="kw">c</span>(<span class="st">'temp'</span>, <span class="st">'humid'</span>, <span class="st">'wind_speed'</span>, <span class="st">'visib'</span>, <span class="st">'pressure'</span>)</span>
<span id="cb265-2"><a href="iterative.html#cb265-2"></a>nyc_means =<span class="st"> </span><span class="kw">numeric</span>()</span>
<span id="cb265-3"><a href="iterative.html#cb265-3"></a></span>
<span id="cb265-4"><a href="iterative.html#cb265-4"></a><span class="cf">for</span> (i <span class="cf">in</span> <span class="kw">seq_along</span>(columns)) {</span>
<span id="cb265-5"><a href="iterative.html#cb265-5"></a> nyc_means[i] =<span class="st"> </span><span class="kw">mean</span>(weather[[columns[i]]], <span class="dt">na.rm =</span> <span class="ot">TRUE</span>)</span>
<span id="cb265-6"><a href="iterative.html#cb265-6"></a>}</span>
<span id="cb265-7"><a href="iterative.html#cb265-7"></a></span>
<span id="cb265-8"><a href="iterative.html#cb265-8"></a>nyc_means <span class="op">%>%</span><span class="st"> </span><span class="kw">round</span>(<span class="dv">2</span>)</span></code></pre></div>
<pre><code>[1] 55.26 62.53 10.52 9.26 1017.90</code></pre>
<p>However, the other approach is slightly faster, because memory is already allocated for all elements of <span class="objclass">nyc_means</span>, rather than updating it every iteration of the loop. This speed gain can become noticeable when dealing with thousands of columns and complex operations.</p>
</div>
<div id="while-alternative" class="section level3">
<h3>While alternative</h3>
<p>When you look at some people’s R code, you may see a loop of a different sort.</p>
<div class="sourceCode" id="cb267"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb267-1"><a href="iterative.html#cb267-1"></a>columns =<span class="st"> </span><span class="kw">c</span>(<span class="st">'temp'</span>,<span class="st">'humid'</span>,<span class="st">'wind_speed'</span>, <span class="st">'visib'</span>, <span class="st">'pressure'</span>)</span>
<span id="cb267-2"><a href="iterative.html#cb267-2"></a>nyc_means =<span class="st"> </span><span class="kw">c</span>()</span>
<span id="cb267-3"><a href="iterative.html#cb267-3"></a></span>
<span id="cb267-4"><a href="iterative.html#cb267-4"></a>i =<span class="st"> </span><span class="dv">1</span></span>
<span id="cb267-5"><a href="iterative.html#cb267-5"></a><span class="cf">while</span> (i <span class="op"><=</span><span class="st"> </span><span class="kw">length</span>(columns)) {</span>
<span id="cb267-6"><a href="iterative.html#cb267-6"></a> nyc_means[i] =<span class="st"> </span><span class="kw">mean</span>(weather[[columns[i]]], <span class="dt">na.rm =</span> <span class="ot">TRUE</span>)</span>
<span id="cb267-7"><a href="iterative.html#cb267-7"></a> i =<span class="st"> </span>i <span class="op">+</span><span class="st"> </span><span class="dv">1</span></span>
<span id="cb267-8"><a href="iterative.html#cb267-8"></a>}</span>
<span id="cb267-9"><a href="iterative.html#cb267-9"></a></span>
<span id="cb267-10"><a href="iterative.html#cb267-10"></a>nyc_means <span class="op">%>%</span><span class="st"> </span><span class="kw">round</span>(<span class="dv">2</span>)</span></code></pre></div>
<pre><code>[1] 55.26 62.53 10.52 9.26 1017.90</code></pre>
<p>This involves a <span class="emph">while</span> statement. It states, while <code>i</code> is less than or equal to the length (number) of <span class="objclass">columns</span>, compute the value of the i<sup>th</sup> element of <span class="objclass">nyc_means</span> as the mean of i<sup>th</sup> column of <span class="objclass">weather</span>. After that, increase the value of <code>i</code>. So, we start with <code>i = 1</code>, compute that subsequent mean, <code>i</code> now equals 2, do the process again, and so on. The process will stop as soon as the value of <code>i</code> is greater than the length of <span class="objclass">columns</span>.</p>
<p><em>There is zero difference to using the while approach vs. the for loop</em>. While is often used when there is a check to be made, e.g. in modeling functions that have to stop the estimation process at some point, or else they’d go on indefinitely. In that case the while syntax is probably more natural. Either is fine.</p>
</div>
<div id="loops-summary" class="section level3">
<h3>Loops summary</h3>
<p>Understanding loops is fundamental toward spending less time processing data and more time toward exploring it. Your code will be more succinct and more able to handle the usual changes that come with dealing with data. Now that you have a sense of it, know that once you are armed with the sorts of things we’ll be talking about next- apply functions, writing functions, and vectorization - you’ll likely have little need to write explicit loops. While there is always a need for iterative processing of data, R provides even more efficient means to do so.</p>
</div>
</div>
<div id="implicit-loops" class="section level2">
<h2>Implicit Loops</h2>
<p>Writing loops is straightforward once you get the initial hang of it. However, R offers alternative ways to do loops that can simplify code without losing readability. As such, even when you loop in R, you don’t have to do so explicitly.</p>
<div id="apply-family" class="section level3">
<h3>apply family</h3>
<p>A family of functions comes with R that allows for a succinct way of looping when it is appropriate. Common functions in this family include:</p>
<ul>
<li><span class="func">apply</span>
<ul>
<li>arrays, matrices, data.frames</li>
</ul></li>
<li><span class="func">lapply</span>, <span class="func">sapply</span>, <span class="func">vapply</span>
<ul>
<li>lists, data.frames, vectors</li>
</ul></li>
<li><span class="func">tapply</span>
<ul>
<li>grouped operations (table apply)</li>
</ul></li>
<li><span class="func">mapply</span>
<ul>
<li>multivariate version of sapply</li>
</ul></li>
<li><span class="func">replicate</span>
<ul>
<li>performs an operation N times</li>
</ul></li>
</ul>
<p>As an example we’ll consider standardizing variables, i.e. taking a set of numbers, subtracting the mean, and dividing by the standard deviation. This results in a variable with mean of 0 and standard deviation of 1. Let’s start with a loop approach.</p>
<div class="sourceCode" id="cb269"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb269-1"><a href="iterative.html#cb269-1"></a><span class="cf">for</span> (i <span class="cf">in</span> <span class="dv">1</span><span class="op">:</span><span class="kw">ncol</span>(mydf)) {</span>
<span id="cb269-2"><a href="iterative.html#cb269-2"></a> x =<span class="st"> </span>mydf[, i]</span>
<span id="cb269-3"><a href="iterative.html#cb269-3"></a> <span class="cf">for</span> (j <span class="cf">in</span> <span class="dv">1</span><span class="op">:</span><span class="kw">length</span>(x)) {</span>
<span id="cb269-4"><a href="iterative.html#cb269-4"></a> x[j] =<span class="st"> </span>(x[j] <span class="op">-</span><span class="st"> </span><span class="kw">mean</span>(x)) <span class="op">/</span><span class="st"> </span><span class="kw">sd</span>(x)</span>
<span id="cb269-5"><a href="iterative.html#cb269-5"></a> }</span>
<span id="cb269-6"><a href="iterative.html#cb269-6"></a>}</span></code></pre></div>
<p>The above would be a really bad way to use R. It goes over each column individually, then over each value of the column.</p>
<p>Conversely, <span class="func">apply</span> will take a matrix or data frame, and apply a function over the margin, row or column, you want to loop over. The first argument is the data you’re considering, the margin is the second argument (1 for rows, 2 for columns<a href="#fn12" class="footnote-ref" id="fnref12"><sup>12</sup></a>), and the function you want to apply to those rows is the third argument. The following example is much cleaner compared to the loop, and now you’d have a function you can use elsewhere if needed.</p>
<div class="sourceCode" id="cb270"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb270-1"><a href="iterative.html#cb270-1"></a>stdize <-<span class="st"> </span><span class="cf">function</span>(x) {</span>
<span id="cb270-2"><a href="iterative.html#cb270-2"></a> (x <span class="op">-</span><span class="st"> </span><span class="kw">mean</span>(x)) <span class="op">/</span><span class="st"> </span><span class="kw">sd</span>(x)</span>
<span id="cb270-3"><a href="iterative.html#cb270-3"></a>}</span>
<span id="cb270-4"><a href="iterative.html#cb270-4"></a></span>
<span id="cb270-5"><a href="iterative.html#cb270-5"></a><span class="kw">apply</span>(mydf, <span class="dv">2</span>, stdize) <span class="co"># 1 for rows, 2 for columnwise application</span></span></code></pre></div>
<p>Many of the other apply functions work similarly, taking an object and a function to do the work on the object (possibly implicit), possibly with other arguments specified if necessary.</p>
<div id="lapply" class="section level4">
<h4>lapply</h4>
<p>Let’s say we have a list object, or even just a vector of values. There are no rows or columns to iterate over, so what do we do here?</p>
<div class="sourceCode" id="cb271"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb271-1"><a href="iterative.html#cb271-1"></a>x =<span class="st"> </span><span class="kw">list</span>(<span class="st">'aba'</span>, <span class="st">'abb'</span>, <span class="st">'abc'</span>, <span class="st">'abd'</span>, <span class="st">'abe'</span>)</span>
<span id="cb271-2"><a href="iterative.html#cb271-2"></a></span>
<span id="cb271-3"><a href="iterative.html#cb271-3"></a><span class="kw">lapply</span>(x, str_remove, <span class="dt">pattern =</span> <span class="st">'ab'</span>)</span></code></pre></div>
<pre><code>[[1]]
[1] "a"
[[2]]
[1] "b"
[[3]]
[1] "c"
[[4]]
[1] "d"
[[5]]
[1] "e"</code></pre>
<p>The <span class="func">lapply</span> operation iterates over each element of the list and applies a function to them. In this case, the function is <span class="func">str_remove</span>. It has an argument for the string pattern we want to take out of the character string that is fed to it (‘ab’). For example, for ‘aba’ we will be left with just the ‘a’.</p>
<p>As can be seen, <span class="func">lapply</span> starts with a <span class="objclass">list</span> and returns a <span class="objclass">list</span>. The only difference with <span class="func">sapply</span> is that <span class="func">sapply</span> will return a simplified form if possible<a href="#fn13" class="footnote-ref" id="fnref13"><sup>13</sup></a>.</p>
<div class="sourceCode" id="cb273"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb273-1"><a href="iterative.html#cb273-1"></a><span class="kw">sapply</span>(x, str_remove, <span class="dt">pattern =</span> <span class="st">'ab'</span>)</span></code></pre></div>
<pre><code>[1] "a" "b" "c" "d" "e"</code></pre>
<p>In this case we just get a vector back.</p>
</div>
</div>
<div id="apply-functions" class="section level3">
<h3>Apply functions</h3>
<p>It is important to be familiar with the apply family for efficient data processing, if only because you’ll regularly come code employing these functions. A summary of benefits includes:</p>
<ul>
<li>Cleaner/simpler code</li>
<li>Environment kept clear of unnecessary objects</li>
<li>Potentially more reproducible
<ul>
<li>more likely to use generalizable functions</li>
</ul></li>
<li>Parallelizable</li>
</ul>
<p>Note that apply functions are <span class="emph">NOT</span> necessarily faster than explicit loops, and if you create an empty object for the loop as discussed previously, the explicit loop will likely be faster. On top of that, functions like <span class="func">replicate</span> and <span class="func">mapply</span> are especially slow.</p>
<p>However, the apply family can ALWAYS <em>potentially</em> be faster than standard R loops do to parallelization. With base R’s <span class="pack">parallel</span> package, there are parallel versions of the apply family, e.g.<span class="func">parApply</span>, <span class="func">parLapply</span> etc. As every modern computer has at least four cores to play with, you’ll always potentially have nearly a 4x speedup by using the parallel apply functions.</p>
<p>Apply functions and similar approaches should be a part of your regular R experience. We’ll talk about other options that may have even more benefits, but you need to know the basics of how apply functions work in order to use those.</p>
<div class="note">
<p>I use R every day, and very rarely use explicit loops. Note that there is no speed difference for a <span class="func">for</span> loop vs. using <span class="func">while</span>. And if you must use an explicit loop, create an empty object of the dimension/form you need, and then fill it in via the loop. This will be notably faster.</p>
<p>I pretty much never use an explicit double loop, as a little more thinking about the problem will usually provide a more efficient path to solving the problem.</p>
<p><img class='img-note' src="img/R.ico" style="display:block; margin: 0 auto;"></p>
</div>
</div>
<div id="purrr" class="section level3">
<h3>purrr</h3>
<p>The <span class="pack">purrr</span> package allows you to take the <span class="func">apply</span> family approach to the tidyverse. And with packages <span class="pack" style="">future</span> + <span class="pack" style="">furrr</span>, they too are parallelizable.</p>
<p>Consider the following. We’ll use the <span class="func">map</span> function to map the <span class="func">sum</span> function to each element in the list, the same way we would with <span class="func">lapply</span>.</p>
<div class="sourceCode" id="cb275"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb275-1"><a href="iterative.html#cb275-1"></a>x =<span class="st"> </span><span class="kw">list</span>(<span class="dv">1</span><span class="op">:</span><span class="dv">3</span>, <span class="dv">4</span><span class="op">:</span><span class="dv">6</span>, <span class="dv">7</span><span class="op">:</span><span class="dv">9</span>)</span>
<span id="cb275-2"><a href="iterative.html#cb275-2"></a></span>
<span id="cb275-3"><a href="iterative.html#cb275-3"></a><span class="kw">map</span>(x, sum)</span></code></pre></div>
<pre><code>[[1]]
[1] 6
[[2]]
[1] 15
[[3]]
[1] 24</code></pre>
<p>The map functions take some getting used to, and in my experience they are typically slower than the apply functions, sometimes notably so. However they allow you stay within the tidy realm, which has its own benefits, and have more control over the nature of the output<a href="#fn14" class="footnote-ref" id="fnref14"><sup>14</sup></a>, which is especially important in reproducibility, package development, producing production-level code, etc. The key idea is that the map functions will always return something the same length as the input given to it.</p>
<p>The <span class="pack">purrr</span> functions want a list or vector, i.e. they don’t work with data.frame objects in the same way we’ve done with mutate and summarize except in the sense that data.frames are lists.</p>
<div class="sourceCode" id="cb277"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb277-1"><a href="iterative.html#cb277-1"></a><span class="co">## mtcars %>% </span></span>
<span id="cb277-2"><a href="iterative.html#cb277-2"></a><span class="co">## map(scale) # returns a list, not shown</span></span>
<span id="cb277-3"><a href="iterative.html#cb277-3"></a></span>
<span id="cb277-4"><a href="iterative.html#cb277-4"></a>mtcars <span class="op">%>%</span><span class="st"> </span></span>
<span id="cb277-5"><a href="iterative.html#cb277-5"></a><span class="st"> </span><span class="kw">map_df</span>(scale) <span class="co"># returns a df</span></span></code></pre></div>
<pre><code># A tibble: 32 x 11
mpg[,1] cyl[,1] disp[,1] hp[,1] drat[,1] wt[,1] qsec[,1] vs[,1] am[,1] gear[,1] carb[,1]
<dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
1 0.151 -0.105 -0.571 -0.535 0.568 -0.610 -0.777 -0.868 1.19 0.424 0.735
2 0.151 -0.105 -0.571 -0.535 0.568 -0.350 -0.464 -0.868 1.19 0.424 0.735
3 0.450 -1.22 -0.990 -0.783 0.474 -0.917 0.426 1.12 1.19 0.424 -1.12
4 0.217 -0.105 0.220 -0.535 -0.966 -0.00230 0.890 1.12 -0.814 -0.932 -1.12
5 -0.231 1.01 1.04 0.413 -0.835 0.228 -0.464 -0.868 -0.814 -0.932 -0.503
6 -0.330 -0.105 -0.0462 -0.608 -1.56 0.248 1.33 1.12 -0.814 -0.932 -1.12
7 -0.961 1.01 1.04 1.43 -0.723 0.361 -1.12 -0.868 -0.814 -0.932 0.735
8 0.715 -1.22 -0.678 -1.24 0.175 -0.0278 1.20 1.12 -0.814 0.424 -0.503
9 0.450 -1.22 -0.726 -0.754 0.605 -0.0687 2.83 1.12 -0.814 0.424 -0.503
10 -0.148 -0.105 -0.509 -0.345 0.605 0.228 0.253 1.12 -0.814 0.424 0.735
# … with 22 more rows</code></pre>
<div class="sourceCode" id="cb279"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb279-1"><a href="iterative.html#cb279-1"></a>mtcars <span class="op">%>%</span><span class="st"> </span></span>
<span id="cb279-2"><a href="iterative.html#cb279-2"></a><span class="st"> </span><span class="kw">map_dbl</span>(sum) <span class="co"># returns a numeric (double) vector of column sums</span></span></code></pre></div>
<pre><code> mpg cyl disp hp drat wt qsec vs am gear carb
642.900 198.000 7383.100 4694.000 115.090 102.952 571.160 14.000 13.000 118.000 90.000 </code></pre>
<div class="sourceCode" id="cb281"><pre class="sourceCode r"><code class="sourceCode r"><span id="cb281-1"><a href="iterative.html#cb281-1"></a>diamonds <span class="op">%>%</span></span>
<span id="cb281-2"><a href="iterative.html#cb281-2"></a><span class="st"> </span><span class="kw">map_at</span>(</span>
<span id="cb281-3"><a href="iterative.html#cb281-3"></a> <span class="kw">vars</span>(carat, depth, price),</span>
<span id="cb281-4"><a href="iterative.html#cb281-4"></a> <span class="cf">function</span>(x)</span>
<span id="cb281-5"><a href="iterative.html#cb281-5"></a> <span class="kw">as.integer</span>(x <span class="op">></span><span class="st"> </span><span class="kw">median</span>(x))</span>
<span id="cb281-6"><a href="iterative.html#cb281-6"></a> ) <span class="op">%>%</span><span class="st"> </span></span>