替換字符串/文本中“從第 n 個到最后一個”出現的單詞

Question

這個問題以前曾被問過，但沒有得到讓提問者滿意的答案。

給定以下字符串：

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

以下 function 允許替換其中第 n 次出現的單詞：

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"

我們如何調整這個 function 來替換第 n 個到最后一個出現的單詞？

倒數第二名：

"one fish two dog red dog blue dog"

倒數第三名：

"one fish two fish red dog blue dog"

等等...？

我嘗試了 str_replace_all 或調整正則表達式部分 {1,} 但沒有成功。

謝謝你的幫助！

Answer 1

這是gsubfn的一個更簡單的選擇

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"

Answer 2

您的 function 相當復雜，有條件。 另一種方法是將字符串拆分為單個單詞的字符向量，對其應用stringr函數，然后將其連接回單個字符串：

library(stringr)

replace_function <- function(string, word, rword, n) {
  vec <- unlist(strsplit(string, " "))
  vec[str_which(vec, word)[n]] <- rword
  str_c(vec, collapse = " ")
}

replace_function(mystring, "fish", "dog", 1)
[1] "one dog two fish red fish blue fish"

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

現在，您可以使用rev()非常輕松地修改此 function 以替換最后的第 n 個元素：

replace_end_function <- function(string, word, rword, n) {
  vec <- unlist(strsplit(string, " "))
  vec[rev(str_which(vec, word))[n]] <- rword
  str_c(vec, collapse = " ")
}

replace_end_function(mystring, "fish", "dog", 1)
[1] "one fish two fish red fish blue dog"

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

---

編輯（我認為“倒數第n個”的意思是“倒數第n個”是我的錯）：

要將第 n 個元素替換為最后一個元素：

replace_end_function <- function(string, word, rword, n) {
  vec <- unlist(strsplit(string, " "))
  vec[str_which(vec, word)[n:length(str_which(vec, word))]] <- rword
  str_c(vec, collapse = " ")
}

replace_end_function(mystring, "fish", "dog", 1)
[1] "one dog two dog red dog blue dog"

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

replace_end_function(mystring, "fish", "dog", 3)
[1] "one fish two fish red dog blue dog"

replace_end_function(mystring, "fish", "dog", 4)
[1] "one fish two fish red fish blue dog"

Answer 3

您可以在 function replacerFn中使用grep ，即

replacerFn <- function(String, word, rword, n) {
  v <- unlist(strsplit(String,split = " "))
  v[grep(word,v)[n:length(v)]] <- rword
  return(paste0(v,collapse = " "))
}