Using gsub for a specific occurrence in a string in R?
You could use
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)
which gives
> 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."