使用 Dplyr 在 R 中选择变量（列）

在本文中，我们将使用 dplyr 库在 R 编程语言中选择变量或列。

使用中的数据集：

选择带有列名的列

这里我们将使用 select() 方法按名称选择列

句法：

select(dataframe,column1,column2,.,column n)

这里，数据框是输入数据框，列是要显示的数据框中的列

示例 1： R 程序选择列

R

# load the library
library(dplyr)
  
# create dataframe with 3 columns
# id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush',
                        'sravan','gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali',
                           'vijayawada','vijayawada',
                           'guntur','hyd','tenali','hyd'))
  
# select id column from the dataframe by 
# column name
print(select(data1,id))
    
# select name column from the dataframe by
# column name
print(select(data1,name))

输出：

示例 2 ：R 程序选择多列

电阻

# load the library
library(dplyr)
  
# create dataframe with 3 columns 
# id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush',
                        'sravan','gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali',
                           'vijayawada','vijayawada',
                           'guntur','hyd','tenali','hyd'))
  
# select multiple columns from the dataframe
# by column name
print(select(data1,id,name,address))

输出：

按位置选择列

我们还可以使用列位置并使用 select() 方法获取列。位置从 1 开始。

句法：

select(dataframe,column1_position,column2_position,.,column n_position)

where, dataframe is the input dataframe and column position is an column number

为了选择多列，我们可以使用范围运算符“;”按位置选择列

句法：

select(dataframe,start_position:end_position)

where, dataframe is the input dataframe, start_position  is a column number starting position and end_position  is a column number ending position

示例 1： R 程序按列位置选择特定列

电阻

# load the library
library(dplyr)
  
# create dataframe with 3 columns
# id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush',
                        'sravan','gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali',
                           'vijayawada','vijayawada',
                           'guntur','hyd','tenali','hyd'))
  
# select first column by column position
print(select(data1,1))
  
# select third column by column position
print(select(data1,3))
   

输出：

示例2： R程序按位置选择多列

电阻

# load the library
library(dplyr)
  
# create dataframe with 3 columns 
# id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush','sravan',
                        'gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali',
                           'vijayawada','vijayawada','guntur',
                           'hyd','tenali','hyd'))
  
# select multiple column by column position
print(select(data1,1,2))

输出：

示例 3： R 程序使用范围运算符按位置选择多列

电阻

# load the library
library(dplyr)
  
# create dataframe with 3 columns 
# id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush','sravan',
                        'gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali',
                           'vijayawada','vijayawada','guntur',
                           'hyd','tenali','hyd'))
  
# select multiple column by column 
# position with : operator
print(select(data1,1:3))

输出：

选择包含值或匹配模式的列

在这里，我们将根据列中存在的值或模式显示列值

方法一：使用 contains()

显示包含给定子字符串的列

句法：

select(dataframe,contains(‘sub_string’))

这里，dataframe 是输入数据帧，sub_string 是列名中存在的字符串

示例： R 程序根据子字符串选择列

电阻

# load the library
library(dplyr)
  
# create dataframe with 3 columns 
# id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush','sravan',
                        'gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali',
                           'vijayawada','vijayawada','guntur',
                           'hyd','tenali','hyd'))
  
# select column that contains am
print(select(data1,contains('am')))
  
# select column that contains d
print(select(data1,contains('d')))
  
# select column that contains dd
print(select(data1,contains('dd')))

输出：

方法二：使用matches()

它将检查并显示包含给定子字符串的列

select(dataframe,matches(‘sub_string’))

这里，dataframe 是输入数据帧，sub_string 是列名中存在的字符串

示例： R 程序根据子字符串选择列

电阻

# load the library
library(dplyr)
  
# create dataframe with 3 columns 
# id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush','sravan',
                        'gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali',
                           'vijayawada','vijayawada','guntur',
                           'hyd','tenali','hyd'))
  
# select column that matches with  am
print(select(data1,matches('am')))
  
# select column that matches with d
print(select(data1,matches ('d')))
  
# select column that matches with  dd
print(select(data1,matches ('dd')))

输出：

选择以特定字符开头或结尾的列

在这里我们还可以根据开始和结束字符选择列。

• starts_with()用于返回以给定字符开头的列。

句法：

select(dataframe,starts_with(‘substring’))

Where, dataframe is the input dataframe and substring is the character/string that starts with it

• Ends_with()用于返回以给定字符结尾的列。

句法：

select(dataframe,ends_with(‘substring’))

where, dataframe is the input dataframe and substring is the character/string that ends with it

示例 1： R 程序显示以字符/substring 开头的列

电阻

# load the library
library(dplyr)
  
# create dataframe with 3 columns id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush','sravan',
                        'gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali',
                           'vijayawada','vijayawada','guntur',
                           'hyd','tenali','hyd'))
  
# select column that starts with n
print(select(data1,starts_with('n')))
  
# select column that starts with add
print(select(data1,starts_with('add')))

输出：

示例 2： R 程序选择以给定字符串或字符结尾的列

电阻

# load the library
library(dplyr)
  
# create dataframe with 3 columns id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush','sravan',
                        'gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali','vijayawada',
                           'vijayawada','guntur','hyd','tenali','hyd'))
  
# select column that ends with ss
print(select(data1,ends_with('ss')))
  
# select column that ends with d
print(select(data1,ends_with('d')))

输出：

选择所有列

我们可以使用everything() 方法选择数据框中的所有列。

语法：

select(dataframe,everything())

示例：R 程序选择所有列

电阻

# load the library
library(dplyr)
  
# create dataframe with 3 columns
# id,name and address
data1=data.frame(id=c(1,2,3,4,5,6,7,1,4,2),
                   
                 name=c('sravan','ojaswi','bobby','gnanesh',
                        'rohith','pinkey','dhanush','sravan',
                        'gnanesh','ojaswi'),
                   
                 address=c('hyd','hyd','ponnur','tenali',
                           'vijayawada','vijayawada','guntur',
                           'hyd','tenali','hyd'))
  
# select all columns using everything method
print(select(data1,everything()))

输出：