How to concatenate factors, without them being converted to integer level?

Question

I was surprised to see that R will coerce factors into a number when concatenating vectors. This happens even when the levels are the same. For example:

>         


        

Answer 1

Based on the other answers which use converting to character I'm using the following function to concatenate factors:

concat.factor <- function(...){
  as.factor(do.call(c, lapply(list(...), as.character)))
}

You can use this function just as you would use c.