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

If you really mean DROPing those columns, here is a solution:

library(data.table)
dt <- data.table(x=c(1,2,3,NA,5), 
                 y=c(1,1,NA,NA,NA),
                 z=c(NA,NA,NA,NA,NA), 
                 d=c(2,2,2,2,2))

for (col in names(copy(dt))){
    v = var(dt[[col]], na.rm = TRUE)
    if (v == 0 | is.na(v)) dt[, (col) := NULL]
}