notebooks/Day 1.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Day 1 Recap"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "import pandas as pd\n",
    "import seaborn.apionly as sns\n",
    "import matplotlib.pyplot as plt"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style>\n",
       "    .dataframe thead tr:only-child th {\n",
       "        text-align: right;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: left;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>fl_date</th>\n",
       "      <th>airline_id</th>\n",
       "      <th>tail_num</th>\n",
       "      <th>fl_num</th>\n",
       "      <th>origin</th>\n",
       "      <th>dest</th>\n",
       "      <th>dep_time</th>\n",
       "      <th>dep_delay</th>\n",
       "      <th>arr_time</th>\n",
       "      <th>arr_delay</th>\n",
       "      <th>cancelled</th>\n",
       "      <th>arr</th>\n",
       "      <th>dep</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>unique_carrier</th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>AA</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>19805</td>\n",
       "      <td>N338AA</td>\n",
       "      <td>1</td>\n",
       "      <td>JFK</td>\n",
       "      <td>LAX</td>\n",
       "      <td>914.0</td>\n",
       "      <td>14.0</td>\n",
       "      <td>1238.0</td>\n",
       "      <td>13.0</td>\n",
       "      <td>0.0</td>\n",
       "      <td>2014-01-01 12:38:00</td>\n",
       "      <td>2014-01-01 09:14:00</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>B6</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>20409</td>\n",
       "      <td>N318JB</td>\n",
       "      <td>115</td>\n",
       "      <td>SYR</td>\n",
       "      <td>JFK</td>\n",
       "      <td>720.0</td>\n",
       "      <td>90.0</td>\n",
       "      <td>808.0</td>\n",
       "      <td>55.0</td>\n",
       "      <td>0.0</td>\n",
       "      <td>2014-01-01 08:08:00</td>\n",
       "      <td>2014-01-01 07:20:00</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>DL</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>19790</td>\n",
       "      <td>N930DL</td>\n",
       "      <td>61</td>\n",
       "      <td>LGA</td>\n",
       "      <td>ATL</td>\n",
       "      <td>1810.0</td>\n",
       "      <td>10.0</td>\n",
       "      <td>2054.0</td>\n",
       "      <td>10.0</td>\n",
       "      <td>0.0</td>\n",
       "      <td>2014-01-01 20:54:00</td>\n",
       "      <td>2014-01-01 18:10:00</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>EV</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>20366</td>\n",
       "      <td>N14977</td>\n",
       "      <td>3259</td>\n",
       "      <td>HPN</td>\n",
       "      <td>ORD</td>\n",
       "      <td>731.0</td>\n",
       "      <td>-5.0</td>\n",
       "      <td>940.0</td>\n",
       "      <td>31.0</td>\n",
       "      <td>0.0</td>\n",
       "      <td>2014-01-01 09:40:00</td>\n",
       "      <td>2014-01-01 07:31:00</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>F9</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>20436</td>\n",
       "      <td>N209FR</td>\n",
       "      <td>507</td>\n",
       "      <td>LGA</td>\n",
       "      <td>DEN</td>\n",
       "      <td>1804.0</td>\n",
       "      <td>35.0</td>\n",
       "      <td>2047.0</td>\n",
       "      <td>47.0</td>\n",
       "      <td>0.0</td>\n",
       "      <td>2014-01-01 20:47:00</td>\n",
       "      <td>2014-01-01 18:04:00</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "                  fl_date  airline_id tail_num  fl_num origin dest  dep_time  \\\n",
       "unique_carrier                                                                 \n",
       "AA             2014-01-01       19805   N338AA       1    JFK  LAX     914.0   \n",
       "B6             2014-01-01       20409   N318JB     115    SYR  JFK     720.0   \n",
       "DL             2014-01-01       19790   N930DL      61    LGA  ATL    1810.0   \n",
       "EV             2014-01-01       20366   N14977    3259    HPN  ORD     731.0   \n",
       "F9             2014-01-01       20436   N209FR     507    LGA  DEN    1804.0   \n",
       "\n",
       "                dep_delay  arr_time  arr_delay  cancelled                 arr  \\\n",
       "unique_carrier                                                                  \n",
       "AA                   14.0    1238.0       13.0        0.0 2014-01-01 12:38:00   \n",
       "B6                   90.0     808.0       55.0        0.0 2014-01-01 08:08:00   \n",
       "DL                   10.0    2054.0       10.0        0.0 2014-01-01 20:54:00   \n",
       "EV                   -5.0     940.0       31.0        0.0 2014-01-01 09:40:00   \n",
       "F9                   35.0    2047.0       47.0        0.0 2014-01-01 20:47:00   \n",
       "\n",
       "                               dep  \n",
       "unique_carrier                      \n",
       "AA             2014-01-01 09:14:00  \n",
       "B6             2014-01-01 07:20:00  \n",
       "DL             2014-01-01 18:10:00  \n",
       "EV             2014-01-01 07:31:00  \n",
       "F9             2014-01-01 18:04:00  "
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "flights = pd.read_csv(\"data/ny-flights.csv.gz\",\n",
    "                      parse_dates=[\"fl_date\", \"arr\", \"dep\"])\n",
    "first = flights.groupby(\"unique_carrier\").first()\n",
    "first.head()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Data Structures\n",
    "\n",
    "1. `DataFrame`: 2-dimensional labeled array\n",
    "2. `Series`: 1-dimensional labeled array\n",
    "3. `Index`: label containers"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Indexing"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Use `[]` aka `__getitem__` for selecting just columns"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style>\n",
       "    .dataframe thead tr:only-child th {\n",
       "        text-align: right;\n",
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       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
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       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>origin</th>\n",
       "      <th>dest</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>unique_carrier</th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>AA</th>\n",
       "      <td>JFK</td>\n",
       "      <td>LAX</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>B6</th>\n",
       "      <td>SYR</td>\n",
       "      <td>JFK</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>DL</th>\n",
       "      <td>LGA</td>\n",
       "      <td>ATL</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>EV</th>\n",
       "      <td>HPN</td>\n",
       "      <td>ORD</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>F9</th>\n",
       "      <td>LGA</td>\n",
       "      <td>DEN</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "               origin dest\n",
       "unique_carrier            \n",
       "AA                JFK  LAX\n",
       "B6                SYR  JFK\n",
       "DL                LGA  ATL\n",
       "EV                HPN  ORD\n",
       "F9                LGA  DEN"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "first[['origin', 'dest']].head()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Use `.loc` for label indexing"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
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       "    .dataframe thead tr:only-child th {\n",
       "        text-align: right;\n",
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       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>origin</th>\n",
       "      <th>dest</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>unique_carrier</th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>AA</th>\n",
       "      <td>JFK</td>\n",
       "      <td>LAX</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>DL</th>\n",
       "      <td>LGA</td>\n",
       "      <td>ATL</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "               origin dest\n",
       "unique_carrier            \n",
       "AA                JFK  LAX\n",
       "DL                LGA  ATL"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "first.loc[['AA', 'DL'], ['origin', 'dest']]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Use `.iloc` for positional indexing"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style>\n",
       "    .dataframe thead tr:only-child th {\n",
       "        text-align: right;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: left;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>origin</th>\n",
       "      <th>dest</th>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>unique_carrier</th>\n",
       "      <th></th>\n",
       "      <th></th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>AA</th>\n",
       "      <td>JFK</td>\n",
       "      <td>LAX</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>DL</th>\n",
       "      <td>LGA</td>\n",
       "      <td>ATL</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "               origin dest\n",
       "unique_carrier            \n",
       "AA                JFK  LAX\n",
       "DL                LGA  ATL"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "first.iloc[[0, 2], [4, 5]]"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "All indexers acccept a *boolean mask*"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
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       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>fl_date</th>\n",
       "      <th>unique_carrier</th>\n",
       "      <th>airline_id</th>\n",
       "      <th>tail_num</th>\n",
       "      <th>fl_num</th>\n",
       "      <th>origin</th>\n",
       "      <th>dest</th>\n",
       "      <th>dep_time</th>\n",
       "      <th>dep_delay</th>\n",
       "      <th>arr_time</th>\n",
       "      <th>arr_delay</th>\n",
       "      <th>cancelled</th>\n",
       "      <th>arr</th>\n",
       "      <th>dep</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>29</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>AA</td>\n",
       "      <td>19805</td>\n",
       "      <td>N3EAAA</td>\n",
       "      <td>359</td>\n",
       "      <td>LGA</td>\n",
       "      <td>ORD</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>1.0</td>\n",
       "      <td>NaT</td>\n",
       "      <td>NaT</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>31</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>AA</td>\n",
       "      <td>19805</td>\n",
       "      <td>N542AA</td>\n",
       "      <td>371</td>\n",
       "      <td>LGA</td>\n",
       "      <td>ORD</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>1.0</td>\n",
       "      <td>NaT</td>\n",
       "      <td>NaT</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>195</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>B6</td>\n",
       "      <td>20409</td>\n",
       "      <td>N913JB</td>\n",
       "      <td>1103</td>\n",
       "      <td>JFK</td>\n",
       "      <td>SJU</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>1.0</td>\n",
       "      <td>NaT</td>\n",
       "      <td>NaT</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>209</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>B6</td>\n",
       "      <td>20409</td>\n",
       "      <td>N193JB</td>\n",
       "      <td>518</td>\n",
       "      <td>JFK</td>\n",
       "      <td>BOS</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>1.0</td>\n",
       "      <td>NaT</td>\n",
       "      <td>NaT</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>359</th>\n",
       "      <td>2014-01-01</td>\n",
       "      <td>EV</td>\n",
       "      <td>20366</td>\n",
       "      <td>N17159</td>\n",
       "      <td>4130</td>\n",
       "      <td>SYR</td>\n",
       "      <td>CLE</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>NaN</td>\n",
       "      <td>1.0</td>\n",
       "      <td>NaT</td>\n",
       "      <td>NaT</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "       fl_date unique_carrier  airline_id tail_num  fl_num origin dest  \\\n",
       "29  2014-01-01             AA       19805   N3EAAA     359    LGA  ORD   \n",
       "31  2014-01-01             AA       19805   N542AA     371    LGA  ORD   \n",
       "195 2014-01-01             B6       20409   N913JB    1103    JFK  SJU   \n",
       "209 2014-01-01             B6       20409   N193JB     518    JFK  BOS   \n",
       "359 2014-01-01             EV       20366   N17159    4130    SYR  CLE   \n",
       "\n",
       "     dep_time  dep_delay  arr_time  arr_delay  cancelled arr dep  \n",
       "29        NaN        NaN       NaN        NaN        1.0 NaT NaT  \n",
       "31        NaN        NaN       NaN        NaN        1.0 NaT NaT  \n",
       "195       NaN        NaN       NaN        NaN        1.0 NaT NaT  \n",
       "209       NaN        NaN       NaN        NaN        1.0 NaT NaT  \n",
       "359       NaN        NaN       NaN        NaN        1.0 NaT NaT  "
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "flights[flights.dep.isnull()].head()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Alignment"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "df1 = pd.DataFrame({\"A\": [1, 2, 3]}, index=['a', 'b', 'c'])\n",
    "df2 = pd.DataFrame({\"A\": [2, 4, 6]}, index=['b', 'a', 'd'])"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "data": {
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       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>A</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>a</th>\n",
       "      <td>1</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>b</th>\n",
       "      <td>2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>c</th>\n",
       "      <td>3</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "   A\n",
       "a  1\n",
       "b  2\n",
       "c  3"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style>\n",
       "    .dataframe thead tr:only-child th {\n",
       "        text-align: right;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: left;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>A</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>b</th>\n",
       "      <td>2</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>a</th>\n",
       "      <td>4</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>d</th>\n",
       "      <td>6</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "   A\n",
       "b  2\n",
       "a  4\n",
       "d  6"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Pandas *aligns* by label, then does the operation."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<div>\n",
       "<style>\n",
       "    .dataframe thead tr:only-child th {\n",
       "        text-align: right;\n",
       "    }\n",
       "\n",
       "    .dataframe thead th {\n",
       "        text-align: left;\n",
       "    }\n",
       "\n",
       "    .dataframe tbody tr th {\n",
       "        vertical-align: top;\n",
       "    }\n",
       "</style>\n",
       "<table border=\"1\" class=\"dataframe\">\n",
       "  <thead>\n",
       "    <tr style=\"text-align: right;\">\n",
       "      <th></th>\n",
       "      <th>A</th>\n",
       "    </tr>\n",
       "  </thead>\n",
       "  <tbody>\n",
       "    <tr>\n",
       "      <th>a</th>\n",
       "      <td>5.0</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>b</th>\n",
       "      <td>4.0</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>c</th>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "    <tr>\n",
       "      <th>d</th>\n",
       "      <td>NaN</td>\n",
       "    </tr>\n",
       "  </tbody>\n",
       "</table>\n",
       "</div>"
      ],
      "text/plain": [
       "     A\n",
       "a  5.0\n",
       "b  4.0\n",
       "c  NaN\n",
       "d  NaN"
      ]
     },
     "execution_count": 10,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "df1 + df2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This saves you from ahving to write the join yourself."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Groupby\n",
    "\n",
    "1. Split by some array\n",
    "2. Apply some function\n",
    "3. Combine the results\n",
    "    - `.agg`: 1 output row per input group\n",
    "    - `.transform`: 1 output row per input row"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "unique_carrier\n",
       "AA    13.044583\n",
       "B6    30.479133\n",
       "DL    29.188422\n",
       "EV    26.735965\n",
       "F9    22.906250\n",
       "FL    24.292553\n",
       "HA    41.241379\n",
       "MQ    20.540419\n",
       "OO    45.000000\n",
       "UA    13.470244\n",
       "US     2.636301\n",
       "VX    17.387543\n",
       "WN    24.854691\n",
       "Name: dep_delay, dtype: float64"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "flights.groupby(\"unique_carrier\").dep_delay.mean()"
   ]
  }
 ],
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