替换字符串/文本中出现的“从第 n 个到最后一个"单词 [英] Replace 'from nth to the last' occurrence of word in string/text

问题描述

这个之前已经问过这个问题，但没有得到提问者满意的回答.

给定以下字符串:

mystring <- "one fish two fish red fish blue fish"

以下函数允许替换其中第 n 次出现的单词:

The following function allows to replace the nth occurrence of a word in it:

replacerFn <- function(String, word, rword, n){
 stopifnot(n >0)
  pat <- sprintf(paste0("^((.*?\\b", word, "\\b.*?){%d})\\b",
           word,"\\b"), n-1)
  rpat <- paste0("\\1", rword)
  if(n >1) { 
    stringr::str_replace(String, pat, rpat)
   } else {
    stringr::str_replace(String, word, rword)
    }
 }


 replacerFn(mystring, "fish", "dog", 1)
 #[1] "one dog two fish red fish blue fish"
 replacerFn(mystring, "fish", "dog", 2)
 #[1] "one fish two dog red fish blue fish"
 replacerFn(mystring, "fish", "dog", 3)
 #[1] "one fish two fish red dog blue fish"
 replacerFn(mystring, "fish", "dog", 4)
 #[1] "one fish two fish red fish blue dog"

我们如何调整这个函数来替换第 n 次到最后一次出现的单词?

How do we have to adjust this function to replace the nth to last occurrence of the word?

倒数第二:

"one fish two dog red dog blue dog"

倒数第三:

"one fish two fish red dog blue dog"

等等......?

我尝试了 str_replace_all 或调整正则表达式部分 {1,} 之类的方法，但没有成功.

I tried things like str_replace_all or adjusting the regex part {1,} but without success.

感谢您的帮助！

推荐答案

这里有一个更简单的选项 gsubfn

Here is an easier option with gsubfn

library(gsubfn)
replacerFn2 <- function(String, word, rword, n) {

  p <- proto(fun = function(this, x) if (count >= n) rword else x) 
   gsubfn(word, p, String)
 }

replacerFn2(mystring, "fish", "dog", 2)
#[1] "one fish two dog red dog blue dog"

replacerFn2(mystring, "fish", "dog", 3)
#[1] "one fish two fish red dog blue dog"
replacerFn2(mystring, "fish", "dog", 4)
#[1] "one fish two fish red fish blue dog"

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