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I have two strings:
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.")
I want to change the third occurrence of the word cat in both strings to dog.
Ideally, string1 and string2 would read:
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."
What is the best way of doing this? Up until now I have only used gsub to replace characters but I don't know if this can be used to replace specific occurrences of a character.
798
The gsub() function in R is used to replace the strings with input strings or values. Note that, you can also use the regular expression with gsub() function to deal with numbers. This is data that has 'R' written multiple times.
We can replace all occurrences of a particular character using gsub() function. Parameters: string is the input string.
To be able to use special characters within a function such as gsub, we have to add two backslashes (i.e. \\) in front of the special character.
How to replace a single character in a string on the R DataFrame column (find and replace)? To replace a first or all occurrences of a single character in a string use gsub(), sub(), str_replace(), str_replace_all() and functions from dplyr package of 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."
You can use 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."
Or, if it needs to be surrounded by word boundaries,
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."
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