Quickly remove zero variance variables from a data.frame

Question

I have a large data.frame that was generated by a process outside my control, which may or may not contain variables with zero variance (i.e. all the observations are the sa

Answer 1

Simply don't use table - it's extremely slow on numeric vectors since it converts them to strings. I would probably use something like

var0 <- unlist(lapply(df, function(x) 0 == var(if (is.factor(x)) as.integer(x) else x)))

It will be TRUE for 0-variance, NA for columns with NAs and FALSE for non-zero variance