R dplyr：通过向量定义的多个正则表达式表达式过滤数据 [英] R dplyr: Filter data by multiple Regex expressions defined by vector

问题描述

我有一个数据框，我想从中选择重要的列，然后过滤行以包含特定的结尾。

I have a dataframe, from which I want to select important columns, and then filter the rows to contain specific ending.

正则表达式使定义我的行变得简单最终值使用 xx $ 符号。但是，如何在多个可能的结尾（ xx $，yy $ ）之间变化？

Regex expression make it simple to define my ending value using xx$ symbol. But, how to vary over multiple possible endings (xx$, yy$)?

虚拟示例：

require(dplyr)

x <- c("aa", "aa", "aa", "bb", "cc", "cc", "cc")
y <- c(101, 102, 113, 201, 202, 344, 407)
type = rep("zz", 7)
df = data.frame(x, y, type)    

# Select all expressions that starts end by "7"
df %>%
  select(x, y) %>%
  filter(grepl("7$", y))

# It seems working when I explicitly define my variables, but I need to use it as a vector instead of values?
df %>%
  select(x, y) %>%
  filter(grepl("[2|7]$", y))  # need to modify this using multiple endings


# How to modify this expression, to use vector of endings (ids) instead?
ids = c(7,2)     # define vector of my values

df %>%
     select(x, y) %>%
     filter(grepl("ids$", y))  # how to change "grepl(ids, y)??"

预期输出：

   x   y type
1 aa 102   zz
2 cc 202   zz
3 cc 407   zz

基于此问题的示例：正则表达式（RegEx）和dplyr :: filter（）

推荐答案

您可以使用

df %>% 
  select(x, y) %> filter(grepl(paste0("(?:", paste(ids, collapse="|"), ")$"), y))

paste0（（?:，paste（ids，crash = |），）$）部分将构建一个交替模式，该模式仅在字符串的末尾匹配，这是由于末尾的 $ 锚点。

The paste0("(?:", paste(ids, collapse="|"), ")$") part will build an alternation pattern that will only match at the end of the string due to $ anchor at the end.

注意：如果值可以具有特殊的正则表达式元字符，则需要先转义字符向量中的值：

NOTE: If the values can have special regex metacharacters you need to escape the values in the character vector first:

regex.escape <- function(string) {
  gsub("([][{}()+*^$|\\\\?.])", "\\\\\\1", string)
}
df %>% 
      select(x, y) %> filter(grepl(paste0("(?:", paste(regex.escape(ids), collapse="|"), ")$"), y))
                                                       ^^^^^^^^^^^^^^^^^

例如， paste0（（ ？：，paste（c（ 7， 8， ids），collapse = |），）$）将输出 （?: 7 | 8 | ids）$ ：

• （？：-一个非捕获组的开始，它将充当替代方案的容器，因此 $ 锚不仅适用于所有锚，还适用于所有锚，与任何


• 
  匹配
  • 7 -a 7 char
  
  
  • (?: - start of a non-capturing group that will act as a container for the alternatives, so that the $ anchor applied to all of them and not to just the last one, matching any of
  • • 7 - a 7 char

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