ch14.Rmd

---
title: "使用 dplyr 套件整理資料"
author: "郭耀仁"
date: "`r Sys.Date()`"
output: slidy_presentation
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE, warning = FALSE, results = 'hide', message = FALSE)
```

## 安裝與載入

```
install.packages("dplyr")
```

```{r}
library(dplyr)
```

## 不同的函數

|函數|用途|
|:----|:----|
|`filter()`|觀測值（列）選擇|
|`select()`|變數（欄）選擇|
|`mutate()`|新增變數（欄）|
|`arrange()`|排序|
|`summarise()`|聚合|
|`group_by()`|分組|

## `filter()`

- 選出女性船員

```{r}
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
filter(straw_hat_df, gender == "Female")
```

## `filter()`（2）

- 選出女性船員並且年紀大於等於 30 歲

```{r}
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
filter(straw_hat_df, gender == "Female" & age >= 30)
```

## `select()`

- 選擇資料框中的變數

```{r}
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
select(straw_hat_df, name, gender)
```

## 使用 `%>%` 運算子

- 可以操作成像是 SQL 的查詢指令

```{r}
# 選出女性船員，但只回傳 name 變數
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
straw_hat_df %>%
  filter(gender == "Female") %>%
  select(name)
```

## `mutate()`

- 新增出生年（`birth_year`）變數
- 利用系統日期減去年紀

```{r}
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
straw_hat_df %>%
  mutate(birth_year = as.integer(format(Sys.Date(), "%Y")) - age)
```

## `arrange()`

- 新增出生年（`birth_year`）變數後以出生年排序

```{r}
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
straw_hat_df %>%
  mutate(birth_year = as.integer(format(Sys.Date(), "%Y")) - age) %>%
  arrange(birth_year)
  # arrange(desc(birth_year))
```

## `summarise()`

- 計算聚合變數平均年齡 `mean_age`

```{r}
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
summarise(straw_hat_df, mean_age = mean(age))
```

## `group_by()`

- 依照性別計算平均年齡 `mean_age`

```{r}
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
straw_hat_df %>%
  group_by(gender) %>%
  summarise(mean_age = mean(age))
```

## `join` 系列函數

|種類|函數|
|----|----|
|內部連結|`inner_join()`|
|左外部連結|`left_join()`|
|右外部連結|`right_join()`|
|全外部連結|`full_join()`|

## `inner_join()`

```{r}
library(dplyr)

# 左表格 straw_hat_df
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
# 右表格 straw_hat_devil_fruit
load(url("https://storage.googleapis.com/r_rookies/straw_hat_devil_fruit.RData"))

# 內部連結
joined_df <- inner_join(straw_hat_df, straw_hat_devil_fruit)
```

## `left_join()`

```{r}
library(dplyr)

# 左表格 straw_hat_df
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
# 右表格 straw_hat_devil_fruit
load(url("https://storage.googleapis.com/r_rookies/straw_hat_devil_fruit.RData"))

# 左外部連結
joined_df <- left_join(straw_hat_df, straw_hat_devil_fruit)
```

## `right_join()`

```{r}
library(dplyr)

# 左表格 straw_hat_df
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
# 右表格 straw_hat_devil_fruit
load(url("https://storage.googleapis.com/r_rookies/straw_hat_devil_fruit.RData"))

# 右外部連結
joined_df <- right_join(straw_hat_df, straw_hat_devil_fruit)
```

## `full_join()`

```{r}
library(dplyr)

# 左表格 straw_hat_df
load(url("https://storage.googleapis.com/r_rookies/straw_hat_df.RData"))
# 右表格 straw_hat_devil_fruit
load(url("https://storage.googleapis.com/r_rookies/straw_hat_devil_fruit.RData"))

# 全外部連結
joined_df <- full_join(straw_hat_df, straw_hat_devil_fruit)
```