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SD/2.3_datatransform/index.qmd

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+---
+title: "Data Transform"
+format:
+  dwsd-revealjs:
+    logo: _extensions/drwater/dwsd/inst/ucaslogo.png
+---
+
+```{r}
+#| echo: false
+source("../../coding/_common.R")
+library(nycflights13)
+library(tidyverse)
+```
+
+
+## `tidyverse`风格数据分析总体流程
+
+![](../../image/data-science/transform.png) 
+
+
+## [dplyr cheatsheet](../../image/cheatsheet/data-transformation.pdf)
+
+
+```{r}
+#| echo: false
+dwfun::ggsavep("../../image/cheatsheet/data-transformation.svg", loadit = TRUE)
+```
+
+
+
+## 查看数据
+
+```{r}
+flights
+```
+
+
+## 选择列
+
+```{r}
+#| results: false
+
+flights |>
+  select(year, month, day)
+```
+
+## 选择列
+
+```{r}
+#| results: false
+
+flights |>
+  select(year:day)
+```
+
+
+## 选择列
+
+```{r}
+flights |>
+  select(3:5)
+```
+
+## 选择列
+
+```{r}
+flights |>
+  select(!year:day)
+```
+
+## 选择列
+
+```{r}
+flights |>
+  select(-(year:day))
+```
+
+## 选择列
+
+```{r}
+flights |>
+  select(where(is.character))
+```
+
+## 选择列
+
+```{r}
+flights |>
+  select(!where(is.character)) |>
+  select(contains("_"))
+```
+
+## 选择列
+
+```{r}
+flights |>
+  select(tail_num = tailnum)
+```
+
+## 选择列
+
+```{r}
+flights |>
+  select(air_time, everything())
+```
+
+
+## 重命名
+
+```{r}
+flights |>
+  rename(tail_num = tailnum)
+```
+
+## 重命名
+
+```{r}
+flights |>
+  rename(年份 = 1) |>
+  rename(月份 = 2)
+```
+
+## 重命名
+
+```{r}
+flights |> select(1:4) |> head(n = 3)
+# 重命名
+flights |> select(1:4) |> head(n = 3) |> rename_all(~ c("c1", "c2", "c3", "c4"))
+```
+
+## 重命名
+
+```{r}
+flights |> select(1:4) |> head(n = 3)
+# 重命名
+flights |> select(1:4) |> head(n = 3) |> rename_all(toupper)
+```
+
+
+## 重命名
+
+```{r}
+flights |> select(1:4) |> head(n = 3)
+# 重命名
+flights |>
+  select(1:4) |>
+  head(n = 3) |>
+  rename_all(~ paste0(toupper(.), "_NEW"))
+```
+
+
+## 练习
+
+将含有下划线的列名中的下划线去掉。
+
+
+```{r}
+flights |> select(1:4) |> head(n = 3)
+```
+
+
+## 练习
+
+将`airqualitydf`中列名的单位信息去除（前5列）。
+
+
+```{r}
+airqualitydf <- readxl::read_xlsx("../../data/airquality.xlsx", sheet = 2)
+airqualitydf |> select(1:5)
+```
+
+
+
+## `filter`
+
+```{r}
+flights |>
+  filter(dep_delay > 120)
+```
+
+## filter 练习
+
+Flights that departed on January 1.
+
+```{r}
+#| echo: false
+flights |>
+  filter(month == 1 & day == 1)
+```
+
+## filter 练习
+
+
+Select flights that departed in January or February
+
+```{r}
+#| echo: false
+flights |>
+  filter(month %in% c(1, 2))
+```
+
+## filter 练习
+
+```{r}
+jan1 <- flights |>
+  filter(month == 1 & day == 1)
+```
+
+## filter
+
+```{r}
+#| error: true
+#| eval: false
+
+flights |>
+  filter(month = 1)
+```
+
+## filter
+
+```{r}
+flights |>
+  filter(month == 1 | 2)
+```
+
+## 排序
+
+```{r}
+flights |>
+  arrange(year, month, day, dep_time)
+```
+
+## 排序
+
+```{r}
+flights |>
+  arrange(desc(dep_delay))
+```
+
+## slice
+
+```{r}
+flights |> head(n = 5)
+flights |> slice(1:5)
+```
+
+## slice
+
+```{r}
+flights |>
+  slice_max(dep_delay, n = 5)
+```
+
+## slice
+
+```{r}
+flights |>
+  slice_min(dep_delay, prop = 0.005)
+```
+
+## 排序练习
+
+根据`origin`、`dest`、`air_time`倒序排序。
+
+```{r}
+#| echo: false
+flights |>
+  arrange(origin, dest, desc(air_time)) |>
+  select(origin, dest, air_time, everything())
+```
+
+
+## 去重
+
+```{r}
+# Remove duplicate rows, if any
+flights |>
+  distinct()
+```
+
+## 去重
+
+```{r}
+# Find all unique origin and destination pairs
+flights |>
+  distinct(origin, dest)
+```
+
+## 去重
+
+```{r}
+flights |>
+  distinct(origin, dest, .keep_all = TRUE)
+```
+
+
+
+## 欢迎讨论！{.center}
+
+```{r}
+#| results: 'asis'
+rmdify::slideend(
+  wechat = FALSE,
+  type = "public",
+  tel = FALSE,
+  thislink = "../"
+)
+```
+