gsub return an empty string when no match is found

Question

I\'m using the gsub function in R to return occurrences of my pattern (reference numbers) on a list of text. This works great unless no match is found, in whic

Answer 1

according to the documentation, this is a feature of gsub it returns the input string if there are no matches to the supplied pattern matches returns the entire string.

here, I use the function grepl first to return a logical vector of the presence/absence of the pattern in the given string:

ifelse(grepl(".*(Ref. (\\d+)).*", data), 
      gsub(".*(Ref. (\\d+)).*", "\\1", data), 
      "")

embedding this in a function:

mygsub <- function(x){
     ans <- ifelse(grepl(".*(Ref. (\\d+)).*", x), 
              gsub(".*(Ref. (\\d+)).*", "\\1", x), 
              "")
     return(ans)
}

mygsub(data)