adding NA values to a factor

[bczucz]

As a part of the improved NA handling I would be very glad for a simpler & cleaner way for adding new NA values to a factor.

> x <- factor(1:3)
> fct_c(NA, x)
Error: All elements of `...` must be factors

The following works, but it looks less "tidy":

> fct_c(factor(NA), x)
[1] <NA> 1    2    3   
Levels: 1 2 3

Thanks!
Balint

[hadley]

You can do that (and much more) with vctrs::vec_c():

vctrs::vec_c(NA, factor(1:3))
#> [1] <NA> 1    2    3   
#> Levels: 1 2 3

^{Created on 2020-02-21 by the reprex package (v0.3.0)}

I think at some point we'll eventually retire fct_c() in favour of this function.