NA as a factor level malformed by rbindlist #3915
Description
data.table(V1 = factor(as.character(c(NA, 1:100, NA)), exclude = NULL))
# Error in as.character.factor(x) : malformed factor
data.table(V1 = factor(as.character(c(NA, 1:3, NA)), exclude = NULL))
# V1
# 1: <NA>
# 2: 1
# 3: 2
# 4: 3
# 5: <NA>
Is this the expected behaviour?
Another example here: https://stackoverflow.com/q/58103098/4552295
I'm getting this result with data.table_1.12.2 and R version 3.6.1.