Question

我有一个问题，即如何替换特定位置的字符。例如：

str <- c("abcdccc","hijklccc","abcuioccc")
#I want to replace character "c" which is in position 3 to "X" how can I do that?
#I know the function gsub and substr, but the only idea I have got so far is 
#use if() to make it. How can I do it quickly?
#ideal result
>str
"abXdccc" "hijklccc" "abXuioccc"

Answer 1

有点尴尬，但是您可以根据单个字符的值替换单个字符，例如：

ifelse(substr(str,3,3)=="c", `substr<-`(str,3,3,"X"), str)
#[1] "abXdccc"   "hijklccc"  "abXuioccc"

如果您乐意覆盖该值，则可以使其更整洁：

substr(str[substr(str,3,3)=="c"],3,3) <- "X"
str
#[1] "abXdccc"   "hijklccc"  "abXuioccc"

Answer 2

我想知道您是否可以在这里使用正则表达式前瞻来获取所需内容。

str <- c("abcdccc","hijklccc","abcuioccc")
gsub("(^.{2})(?=c)(.*$)", "\\1X\\2", str, perl = T)

或使用最新邮件建议的正向后视

sub("(?<=^.{2})c", "X", str, perl = TRUE)

这是在寻找匹配c的字母，该字母位于字符串开头的任何两个字符之后。 c替换为X。

(?<=是积极回望的开始

^.{2}表示从字符串开头的任意两个字符

)c是最后一个部分，它必须在两个字符之后为c

[1] "abXcdccc"   "hijklccc"   "abXcuioccc"

如果您想了解有关正则表达式正在使用的更多信息（link）

另外一个通用函数：

switch_letter <- function(x, letter, position, replacement) {
  stopifnot(position > 1)

  pattern <- paste0("(?<=^.{", position - 1, "})", letter)

  sub(pattern, replacement, x, perl = TRUE)

}

switch_letter(str, "c", 3, "X")

Answer 3

您可以将ifelse与gsub一起使用，即

ifelse(substr(str, 3, 3) == 'c', paste0(substring(str, 1, 2),'X', substring(str, 4)), str)
#[1] "abXdccc"   "hijklccc"  "abXuioccc"

Answer 4

这也应该起作用：

str <- c("abcdefg","hijklnm","abcuiowre")
a <- strsplit(str[1], "")[[1]]
a[3] <- "X"
a <- paste(a, collapse = '')
str[1] <- a

Answer 5

这个主意如何？

c2Xon3 <- function(x){sprintf("%s%s%s",substring(x,1,3),gsub("c","X",substring(x,3,3)),substring(x,4,nchar(x)))}
str <- c("abcdccc","hijklccc","abcuioccc")
strNew <- sapply(str,c2Xon3 )

Answer 6

这应该有效

g++ -o tree tree.cc `pkg-config --libs --cflags gtk+-2.0`

如何替换字符串中特定位置的特定字符？

6 个答案: