R/uniqlist.R

In data.table: Extension of `data.frame`

uniqlist = function(l, order = -1L)
{
  # Assumes input list is ordered by each list item (or by 'order' if supplied), and that all list elements are the same length
  # Finds the non-duplicate rows. Was called duplist but now grows vector - doesn't over-allocate result vector and
  # is >2x times faster on numeric types
  # TO DO: Possibly reinstate reverse argument :
  #    FALSE works in the usual duplicated() way,  the first in a sequence of dups, will be FALSE
  #    TRUE has the last in a sequence of dups FALSE (so you can keep the last if that's required)
  # l = list(...)
  if (!is.list(l))
    stopf("l not type list")
  if (!length(l))  return(list(0L))
  ans = .Call(Cuniqlist, l, as.integer(order))
  ans
}

# implemented for returning the lengths of groups obtained from uniqlist (for internal use only)
uniqlengths = function(x, len) {
  # check for type happens in C, but still converting to integer here to be sure.
  ans = .Call(Cuniqlengths, as.integer(x), as.integer(len))
  ans
}