tidyverse按列提取子集之玩转select

来自https://www.datanovia.com/en/lessons/select-data-frame-columns-in-r/学习笔记。

就是从一个数据框中提取子集，是按照什么提取呢？是按照列来提取！主要有pull、select、select_if，还有一些辅助帮助定位的函数如starts_with(), ends_with(), contains(), matches(), one_of()这些函数！最主要的就是select函数！

曾经记录过tidyverse的数据变换，如下：

tidyverse数据处理包

tidyverse实用函数inner_join等

Reshape2包-长宽数据转换之-melt和dcast函数

Required packages

library(tidyverse)

Demo dataset

my_data <- as_tibble(iris)
my_data

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Extract column values as a vector

my_data %>% pull(Species)

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Extract columns as a data table

1.Select column by position

my_data %>% select(1:3)

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my_data %>% select(1,3)

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2.Select columns by names

my_data %>% select(Sepal.Length, Petal.Length)

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my_data %>% select(Sepal.Length:Petal.Length)

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There are several special functions that can be used inside select(): starts_with(), ends_with(), contains(), matches(), one_of(), etc.

先看一下这个数据的列名

> colnames(my_data)
[1] "Sepal.Length" "Sepal.Width"  "Petal.Length" "Petal.Width"  "Species"   

my_data %>% select(starts_with("Petal"))

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my_data %>% select(ends_with("Width"))

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my_data %>% select(contains("etal"))

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my_data %>% select(matches(".t."))#'.'点号用来匹配换行符以外的任意一个字符

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my_data %>% select(one_of(c("Sepal.Length", "Petal.Length")))

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Select column based on a condtion

my_data %>% select_if(is.numeric)

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Remove columns

1.drop columns by position

my_data %>% select(-Sepal.Length, -Petal.Length)

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my_data %>% select(-(Sepal.Length:Petal.Length))

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my_data %>% select(-starts_with("Petal"))

image-20191213225641398

2.drop columns by position

> colnames(my_data)
[1] "Sepal.Length" "Sepal.Width"  "Petal.Length" "Petal.Width"  "Species"  

my_data %>% select(-1)

image-20191213230424304

my_data %>% select(-(1:3))

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my_data %>% select(-1, -3)

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上面就是提取列的全部操作的示例了，记录下来，下次用的时候可以根据示例的结果很方便地查找到函数