将 gsub 用于 R 中字符串中的特定事件？答案

【问题标题】：Using gsub for a specific occurrence in a string in R?将 gsub 用于 R 中字符串中的特定事件？
【发布时间】：2020-06-15 13:34:00
【问题描述】：

我有两个字符串：

mystring1 <- c("hello i am a cat.  just kidding, i'm not a cat i'm a cat.  dogs are the best animal.  not cats!")

mystring2 <- c("hello i am a cat.  just kidding, i'm not a cat i'm a cat.  but i have a cat friend that is a cat.")

我想将两个字符串中第三次出现的单词 cat 更改为 dog。

理想情况下，string1 和 string2 应该是：

mystring1
[1] "hello i am a cat.  just kidding, i'm not a cat i'm a dog.  dogs are the best animal.  not cats!"

mystring2
[1] "hello i am a cat.  just kidding, i'm not a cat i'm a dog.  but i have a cat friend that is a cat."

这样做的最佳方法是什么？到目前为止，我只使用gsub 替换字符，但我不知道这是否可以用于替换特定出现的字符。

【问题讨论】：

试试sub("(.*?cat.*cat.*)cat", "\\1dog", mystring1)

标签： r gsub

【解决方案1】：

你可以使用

mystring1 <- c("hello i am a cat.  just kidding, i'm not a cat i'm a cat.  dogs are the best animal.  not cats!")
mystring2 <- c("hello i am a cat.  just kidding, i'm not a cat i'm a cat.  but i have a cat friend that is a cat who knows a cat knowing a cat.")

sub("((cat.*?){2})\\bcat\\b", "\\1dog", mystring1, perl=TRUE)

给了

> sub("((cat.*?){2})\\bcat\\b", "\\1dog", c(mystring1, mystring2), perl=TRUE)
[1] "hello i am a cat.  just kidding, i'm not a cat i'm a dog.  dogs are the best animal.  not cats!"                                
[2] "hello i am a cat.  just kidding, i'm not a cat i'm a dog.  but i have a cat friend that is a cat who knows a cat knowing a cat."

【讨论】：

最好用\\b's 包围cat
为什么不使用sub("((cat.*?){2})cat", "\\1dog", c(mystring1, mystring2), perl=T)
@ChrisRuehlemann 好点，但 OP 没有要求在一个语句中同时处理两个字符串。

【解决方案2】：

您可以使用gsubfn

library(gsubfn)
p <- proto(fun = function(this, x) if(count == 3) 'dog' else x)
gsubfn('cat', p, c(mystring1, mystring2))

# [1] "hello i am a cat.  just kidding, i'm not a cat i'm a dog.  dogs are the best animal.  not cats!"  
# [2] "hello i am a cat.  just kidding, i'm not a cat i'm a dog.  but i have a cat friend that is a cat."

或者，如果它需要被单词边界包围，

gsubfn('\\bcat\\b', p, c(mystring1, mystring2), perl = TRUE)

# [1] "hello i am a cat.  just kidding, i'm not a cat i'm a dog.  dogs are the best animal.  not cats!"  
# [2] "hello i am a cat.  just kidding, i'm not a cat i'm a dog.  but i have a cat friend that is a cat."

【讨论】：