Extract mentions from a tweet string using recursion

mention_ext.R

#' Extract mentions
#' @description extract all the mentions of other twitter users from a tweet
#' @param txt the text of your tweet
#' @export

mention_ext <- local({
  ment <- rep(NA,150)
  f <- function(txt){
  if(!is.na(txt)){
      n <- regmatches(txt,regexpr('@[a-zA-Z0-9_]{1,15}',txt))
      txt <- unlist(regmatches(txt,regexpr('@[a-zA-Z0-9_]{1,15}',txt),invert=T))[2]
      Recall(txt)
      if(length(n) > 0){
      ment[nchar(txt)+1] <<- n
      ment[!is.na(ment)]
      }
    }
  }
})

### Example from https://twitter.com/jaimedash/status/639872345075650560
tweet <- "@emhrt_ @_inundata @MSFTResearch looks cool -> @authorea Lots of good tools these days!"
m <- mention_ext(tweet)
### Be sure to do rm(m) after you're done otherwise it will just grow

### Maybe I should have used that loop...
mention_loop <- function(txt){
  n <- vector()
  while(!is.na(txt)){
    n <- c(n,regmatches(txt,regexpr('@[a-zA-Z0-9_]{1,15}',txt)))
    txt <- unlist(regmatches(txt,regexpr('@[a-zA-Z0-9_]{1,15}',txt),invert=T))[2]
  }
  return(n)
}

ml <- mention_loop(tweet)

The while way seems better! Tho I guess this a toy example, you could do
regmatches(tweet, gregexpr('@[a-zA-Z0-9_]{1,15}',tweet))

Or stringr::str_extract_all(tweet, '@[a-zA-Z0-9_]{1,15}') ;)