make function as_fasttext, using code from embed_tagspace

[jwijffels]

usefull if you want to build your own training / test dataset

as_fasttext <- function(x, y, label = "__label__"){
  if(is.list(y)){
    targets <- sapply(y, FUN=function(x){
      if(length(x) == 0 || all(is.na(x))){
        return(NA_character_)
      }
      paste(paste(label, x, sep = ""), collapse = " ") 
    })
  }else{
    targets <- ifelse(is.na(y), NA_character_, paste(label, y, sep = ""))
  }
  x <- ifelse(is.na(targets), x, paste(targets, x, sep = " "))
  x
}