rbindlist two data.tables where one has factor and other has character type for a column

Question

I just discovered this warning in my script that was a bit strange.

# Warning message:
# In rbindlist(list(DT.1, DT.2)) : NAs introduced by coercion
         


        

Answer 1

rbindlist is superfast because it doesn't do the checking of rbindfill or do.call(rbind.data.frame,...)

You can use a workaround like this to ensure that factors are coerced to characters.

DT.1 <- data.table(x = factor(letters[1:5]), y = 6:10)
DT.2 <- data.table(x = LETTERS[1:5], y = 11:15)


for(ii in seq_along(DDL)){
  ff <- Filter(function(x) is.factor(DDL[[ii]][[x]]), names(DDL[[ii]]))
  for(fn in ff){
    set(DDL[[ii]], j = fn, value = as.character(DDL[[ii]][[fn]]))
    }
  }
 rbindlist(DDL)

or (less memory efficiently)

rbindlist(rapply(DDL, classes = 'factor', f= as.character, how = 'replace'))