用其他内容替换字符串中第 N 次出现的字符

Question

考虑a = paste(1:10,collapse=", ")结果

a = "1, 2, 3, 4, 5, 6, 7, 8, 9, 10"

我想替换每第 n 次（比如第 4 次）出现的“，”并将其替换为其他内容（比如“\n”）。 所需的输出将是：

"1, 2, 3, 4\n 5, 6, 7, 8\n 9, 10"

我正在寻找使用gsub （或等效的东西）和某种形式的regular expression来实现此目标的代码。

Answer 1

您可以将((?:\\d+, ){3}\\d),替换为\\1\\n

您基本上会捕获所有内容，直到group1中的第四个逗号为止，然后分别用逗号分隔，并用\\1\\n替换，后者将匹配的文本替换为group1文本和换行符，从而提供了预期的结果。

正则表达式演示

R代码演示

gsub("((?:\\d+, ){3}\\d),", "\\1\n", "1, 2, 3, 4, 5, 6, 7, 8, 9, 10")

印刷品

[1] "1, 2, 3, 4\n 5, 6, 7, 8\n 9, 10"

编辑：

为了将上述解决方案推广到任何文本，我们可以将\\d更改为[^,]

新的R代码演示

gsub("((?:[^,]+, ){3}[^,]+),", "\\1\n", "1, 2, 3, 4, 5, 6, 7, 8, 9, 10")
gsub("((?:[^,]+, ){3}[^,]+),", "\\1\n", "a, bb, ccc, dddd, 500, 600, 700, 800, 900, 1000")

输出，

[1] "1, 2, 3, 4\n 5, 6, 7, 8\n 9, 10"
[1] "a, bb, ccc, dddd\n 500, 600, 700, 800\n 900, 1000"

Answer 2

同时使用regex和gsub 。

a = paste(1:10,collapse=", ")
x <- gsub("([^,]*,[^,]*,[^,]*,[^,]*),", '\\1\n', a)
x
#> [1] "1, 2, 3, 4\n 5, 6, 7, 8\n 9, 10"

Answer 3

正则表达式是最好的选择，不过这是没有正则表达式的另一种方法

> str_vec <- strsplit(a, " ")[[1]] 
> where <- seq_along(str_vec) %% 4 == 0
> str_vec[where] <- sub(",", "\n", str_vec[where])
> paste(str_vec, collapse=" ")
[1] "1, 2, 3, 4\n 5, 6, 7, 8\n 9, 10"

Answer 4

regmatches作为另一种选择：

a <- "1, 2, 3, 4, 5, 6, 7, 8, 9, 10"

fn <- ","
rp <- "\n"
n <- 4

regmatches(a, gregexpr(fn, a)) <- list(c(rep(fn,n-1),rp))
a
#[1] "1, 2, 3, 4\n 5, 6, 7, 8\n 9, 10"

作为功​​能：

a <- "1, 2, 3, 4, 5, 6, 7, 8, 9, 10"

replN <- function(x, fn, rp, n) {
    regmatches(x, gregexpr(fn, x)) <- list(c(rep(fn,n-1),rp))
    x
}
replN(a, ",", "\n", 4)
#[1] "1, 2, 3, 4\n 5, 6, 7, 8\n 9, 10

您甚至可以将其扩展为替换参数的向量化：

a = "1, 2, 3, 4, 5, 6, 7, 8, 9, 10"

replN <- function(x,fn,rp,n) {
    sel <- rep(fn, n*length(rp))
    sel[seq_along(rp)*n] <- rp
    regmatches(x, gregexpr(fn, x)) <- list(sel)
    x
}
replN(a, fn=",", rp=c("1st","2nd"), n=4)
#[1] "1, 2, 3, 41st 5, 6, 7, 82nd 9, 10"

Answer 5

这个可以用字符串而不是字符替换。 我做了一个你可以轻松使用的功能:)

此处演示以了解正则表达式

> a = paste(1:10,collapse=", ")
> a
[1] "1, 2, 3, 4, 5, 6, 7, 8, 9, 10"
> # if you want the 2nd occurence
> gsub("(.*?,.*?),(.*)", "\\1\n\\2", a)
[1] "1, 2\n 3, 4, 5, 6, 7, 8, 9, 10"
> # if you want the 3rd occurence
> gsub("(.*?,.*?,.*?),(.*)", "\\1\n\\2", a)
[1] "1, 2, 3\n 4, 5, 6, 7, 8, 9, 10"
> # if you want the 4rd occurence
> gsub("(.*?,.*?,.*?,.*?),(.*)", "\\1\n\\2", a)
[1] "1, 2, 3, 4\n 5, 6, 7, 8, 9, 10"
> # if you want the last occurence
> gsub("(.*,.*),(.*)", "\\1\n\\2", a)
[1] "1, 2, 3, 4, 5, 6, 7, 8, 9\n 10"
> 
> 
> replace.occurence <- function(x, pattern, replacement, which.occu) {
+   if( which.occu == "last" ) {
+     gsub(paste0("(.*", pattern, ".*)", pattern, "(.*)"), paste0("\\1", replacement, "\\2"), x)
+   } else {
+     gsub(paste0("(.*?", paste0(rep(paste0(pattern, ".*?"), which.occu - 1), collapse = ""), ")", pattern, "(.*)"), paste0("\\1", replacement, "\\2"), x)
+   }
+ }
> 
> replace.occurence(a, pattern = ",", replacement = "\n", which.occu = 2)
[1] "1, 2\n 3, 4, 5, 6, 7, 8, 9, 10"
> replace.occurence(a, pattern = ",", replacement = "\n", which.occu = 3)
[1] "1, 2, 3\n 4, 5, 6, 7, 8, 9, 10"
> replace.occurence(a, pattern = ",", replacement = "\n", which.occu = 4)
[1] "1, 2, 3, 4\n 5, 6, 7, 8, 9, 10"
> replace.occurence(a, pattern = ",", replacement = "\n", which.occu = "last")
[1] "1, 2, 3, 4, 5, 6, 7, 8, 9\n 10"
> 
> replace.occurence(a, pattern = ", 3, 4,", replacement = ", 4, 3,", which.occu = 1)
[1] "1, 2, 4, 3, 5, 6, 7, 8, 9, 10"