Remove constant columns with or without NAs

Question

I am trying to get many lm models work in a function and I need to automatically drop constant columns from my data.table. Thus, I want to keep only columns wit

Answer 1

Check if the variance is zero:

df[, sapply(df, var, na.rm = TRUE) != 0, with = FALSE]
#     x
# 1:  1
# 2:  2
# 3:  3
# 4: NA
# 5:  5