dplyr中select（）的contains（）和matchs（）之间的区别 [英] Difference between contains() and matches() for select() in dplyr

问题描述

我决定花一些时间彻底学习dplyr。我刚刚遇到了 select（）函数和它附带的一些辅助函数。

I have decided to spend some time to learn dplyr thoroughly. I have just come across the select() function and some of the helper functions that come with it.

只是玩耍而已，我没有发现包含和匹配之间的任何区别辅助功能。

By just playing around I have failed to find any difference between the contains and matches helper functions.

有人可以提供一个示例说明如何将它们用于不同的目的吗？

Could someone please provide an example of how they can be used for different purposes?

谢谢

推荐答案

区别是匹配可以使用正则表达式作为模式来匹配列名，并 select 来匹配，而包含可以实现子字符串或全名的字面匹配比赛。在？select_helpers 中描述为

The difference is that matches can take regex as pattern to match column names and select while contains does the literal match of substring or full name match. It is described in the ?select_helpers as

contains（）：包含文字字符串。

contains(): Contains a literal string.

matches（）：匹配正则表达式。

matches(): Matches a regular expression.

考虑一个简单的示例，我们要选择具有子字符串的列'col'

Consider a simple example where we want to select columns that have substring 'col'

df1 <- data.frame(colnm = 1:5, col1 = 24, col2 = 46)
df1 %>% 
    select(contains("col"))
#  colnm col1 col2
#1     1   24   46
#2     2   24   46
#3     3   24   46
#4     4   24   46
#5     5   24   46

这里匹配在列名称中按字面上的 col，然后选择那些。如果我们更改匹配条件以匹配'col'，后跟一个或多个数字（ \\d + ）与正则表达式

Here, it matches the 'col' literally in the column names and select those. If we change the matching criteria to match 'col' followed by one or more digits (\\d+) with a regex

df1 %>% 
   select(contains("col\\d+"))
#data frame with 0 columns and 5 rows

如果失败，因为它正在寻找列名子字符串" col\\d + "

if fails, because it is looking for column name substring "col\\d+"

df1 %>%
    select(matches("col\\d+")) 
# col1 col2
#1   24   46
#2   24   46
#3   24   46
#4   24   46
#5   24   46

而个匹配项使用 regex 并匹配这些模式

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