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

Check this custom function. I did not try it on data frames with 100+ variables.

remove_low_variance_cols <- function(df, threshold = 0) {
  n <- Sys.time() #See how long this takes to run
  remove_cols <- df %>%
    select_if(is.numeric) %>%
    map_dfr(var) %>%
    gather() %>% 
    filter(value <= threshold) %>%
    spread(key, value) %>%
    names()

  if(length(remove_cols)) {
    print("Removing the following columns: ")
    print(remove_cols)
  }else {
    print("There are no low variance columns with this threshold")
  }
  #How long did this script take?
  print(paste("Time Consumed: ", Sys.time() - n, "Secs."))
  return(df[, setdiff(names(df), remove_cols)])
}