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data-transformation.qmd
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data-transformation.qmd
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---
title: "Data Transformation"
---
## Introduction
### Prerequisits
```{julia}
using Tidier
```
### penguins
```{julia}
using PalmerPenguins
penguins = DataFrame(PalmerPenguins.load())
```
## Rows
### `@filter()`
```{julia}
@chain penguins begin
@filter(bill_length_mm > 50)
end
```
```{julia}
@chain penguins begin
@filter(island == "Biscoe" && sex == "male")
end
```
```{julia}
@chain penguins begin
@filter(island == "Biscoe" || sex == "male")
end
```
```{julia}
@chain penguins begin
@filter(island in ("Biscoe", "Dream"))
end
```
```{julia}
penguins_male = @chain penguins begin
@filter(sex == "male")
end
```
### `@arrange()`
```{julia}
@chain penguins begin
@arrange(sex, body_mass_g, flipper_length_mm)
end
```
```{julia}
@chain penguins begin
@arrange(desc(sex), body_mass_g, flipper_length_mm)
end
```
## `@distinct()`
```{julia}
@chain penguins begin
@distinct()
end
```
Note that `@distinct()` keeps the first occurrence of each unique combination of `species` and `island`.
```{julia}
@chain penguins begin
@distinct(species, island)
end
```
If you only want to keep the columns with unique combinations, then you need to explicitely call `@select()`:
```{julia}
# TODO: @select() appears here before it is actually introduced below!
@chain penguins begin
@distinct(species, island)
@select(species, island)
end
```
## Columns
### `@mutate()`
The purpose of `@mutate()` is to add new colums that are calculated from existing colums.
```{julia}
@chain penguins begin
@mutate(
bill_ratio_mm = bill_length_mm / bill_depth_mm
)
end
```
Note that it is not possible to refer to newly created columns in the same `@mutate()` call, but it is possible to chain them:
```{julia}
@chain penguins begin
@mutate(
bill_ratio_mm = bill_length_mm / bill_depth_mm
)
@mutate(
bill_ratio_mm_2 = bill_ratio_mm * 2
)
end
```
### `@select()`
```{julia}
@chain penguins begin
@select(species, island, bill_length_mm)
end
```
```{julia}
@chain penguins begin
@select(species:bill_length_mm)
end
```
```{julia}
@chain penguins begin
@select(!bill_length_mm)
end
```
```{julia}
#| eval: false
# TODO: where() is not defined yet!
@chain penguins begin
@select(where(is_string))
end
```
- `starts_with("abc")`: matches names that begin with “abc” -> supported
- `ends_with("xyz")`: matches names that end with “xyz” -> supported
- `contains("ijk")`: matches names that contain “ijk” -> supported
- `num_range("x", 1:3)`: matches x1, x2 and x3 -> NOT supported
```{julia}
@chain penguins begin
@select(bill_depth = bill_depth_mm)
end
```
### `@rename()`
```{julia}
@chain penguins begin
@rename(bill_depth = bill_depth_mm,
bill_length = bill_length_mm)
end
```
### `@relocate()`
```{julia}
# TODO: relocate() not defined yet!
```
## The Chain
```{julia}
@chain penguins begin
@filter(island in ("Biscoe", "Dream"))
@mutate(bill_ratio_mm = bill_length_mm / bill_depth_mm)
@select(bill_ratio_mm, sex, species:island)
@arrange(bill_ratio_mm)
end
```
## Groups
### `@group_by()`
```{julia}
@chain penguins begin
@group_by(sex)
end
```
### `@summarize()`
```{julia}
@chain penguins begin
@group_by(island)
@summarize(bill_length_mean = mean(bill_length_mm),
n = n())
end
```
```{julia}
@chain penguins begin
@group_by(island)
@summarize(bill_length_mean = mean(skipmissing(bill_length_mm)),
n = n())
end
```
### `@slice()`
Only slice currently supported, no slice_* functions
```{julia}
@chain penguins begin
@group_by(island)
@slice(1)
end
```
```{julia}
# TODO: @slice() does not respond to positive integers!
@chain penguins begin
@group_by(island)
@arrange(bill_length_mm)
@slice(3)
end
```
### Grouping by multiple variables
```{julia}
@chain penguins begin
@group_by(island, sex)
@summarize(n = n())
end
```
### Ungrouping
```{julia}
@chain penguins begin
@group_by(island, sex)
@summarize(n = n())
@ungroup()
end
```