用于保留大小写模式、大写的正则表达式 [英] regex for preserving case pattern, capitalization

问题描述

是否有一个正则表达式可以在 \U 和 \L 的脉络中保留大小写模式?

Is there a regex for preserving case pattern in the vein of \U and \L?

在下面的示例中，我想将 "date" 转换为 "month"，同时保持 input 中使用的大写>

In the example below, I want to convert "date" to "month" while maintaining the capitalization used in the input

   from        to
  "date" ~~> "month"
  "Date" ~~> "Month"
  "DATE" ~~> "MONTH"

我目前使用三个对 sub 的嵌套调用来完成此操作.

I currently use three nested calls to sub to accomplish this.

input <- c("date", "Date", "DATE")
expected.out <- c("month", "Month", "MONTH")

sub("date", "month", 
  sub("Date", "Month", 
    sub("DATE", "MONTH", input)
  )
)

目标是有一个pattern和一个replace，比如

The goal is to have a single pattern and a single replace such as

gsub("(date)", "\\Umonth", input, perl=TRUE) 

这将产生所需的输出

推荐答案

这是我认为 for 循环是合理的情况之一:

This is one of those occasions when I think a for loop is justified:

input <- rep("Here are a date, a Date, and a DATE",2)
pat <- c("date", "Date", "DATE")
ret <- c("month", "Month", "MONTH")

for(i in seq_along(pat)) { input <- gsub(pat[i],ret[i],input) }
input
#[1] "Here are a month, a Month, and a MONTH" 
#[2] "Here are a month, a Month, and a MONTH"

还有一个由 @flodel 提供的替代方案，通过 Reduce 实现与循环相同的逻辑:

And an alternative courtesy of @flodel implementing the same logic as the loop through Reduce:

Reduce(function(str, args) gsub(args[1], args[2], str), 
       Map(c, pat, ret), init = input)

有关这些选项的一些基准测试，请参阅@TylerRinker 的回答.

For some benchmarking of these options, see @TylerRinker's answer.

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