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

Use fct_c from the forcats package (part of the tidyverse).

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

fct_c isn't fooled by concatenations of factors with discrepant numerical codings:

> x <- as.factor(c('c', 'z'))
> x
[1] c z
Levels: c z
> y <- as.factor(c('a', 'b', 'z'))
> y
[1] a b z
Levels: a b z
> c(x, y)
[1] 1 2 1 2 3
> fct_c(x, y)
[1] c z a b z
Levels: c z a b
> as.numeric(fct_c(x, y))
[1] 1 2 3 4 2