Finding ALL duplicate rows, including “elements with smaller subscripts”

Question

R\'s duplicated returns a vector showing whether each element of a vector or data frame is a duplicate of an element with a smaller subscript. So if rows 3, 4,

Answer 1

Here is @Joshua Ulrich's solution as a function. This format allows you to use this code in the same fashion that you would use duplicated():

allDuplicated <- function(vec){
  front <- duplicated(vec)
  back <- duplicated(vec, fromLast = TRUE)
  all_dup <- front + back > 0
  return(all_dup)
}

Using the same example:

vec <- c("a", "b", "c","c","c") 
allDuplicated(vec) 
[1] FALSE FALSE  TRUE  TRUE  TRUE