How can I keep NA when I change levels

Question

I build a vector of factors containing NA.

my_vec <- factor(c(NA,\"a\",\"b\"),exclude=NULL)
levels(my_vec)
# [1] \"a\" \"b\" NA 

I change on

Answer 1

You have to quote NA, otherwise R treats it as a null value rather than a factor level. Factor levels sort alphabetically by default, but obviously that's not always useful, so you can specify a different order by passing a new list order to levels()

require(plyr)
my_vec <- factor(c("NA","a","b1","b2"))
vec2 <- revalue(my_vec,c("b1"="c","b2"="c"))

#now reorder levels

my_vec2 <- factor(vec2, levels(vec2)[c(1,3,2)])

Levels: a NA c