Keith Keith - 1 month ago 23
R Question

how to concatenate factors?

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:

> facs <- as.factor(c("i", "want", "to", "be", "a", "factor", "not", "an", "integer"))
> facs
[1] i want to be a factor not an integer
Levels: a an be factor i integer not to want
> c(facs[1 : 3], facs[4 : 5])
[1] 5 9 8 3 1


what is the idiomatic way to do this in R (in my case these vectors can be pretty large)? Thank you.

Answer

From the R Mailing list:

unlist(list(facs[1 : 3], facs[4 : 5]))

To 'cbind' factors, do

data.frame(facs[1 : 3], facs[4 : 5])