REBOL [ File: %duplicates.r Date: 03-03-2016 Author: "Christian Le Corre" Title: "Duplicates" Purpose: {Get duplicated values in a block} ] duplicates: func [param [block!] /sole /local output][ output: make block! [] loop length? param [ if found? find (next param) param/1 [append output param/1] param: next param ] either sole [unique output][output] ] probe duplicates [1 1 2 3 4 4 4 5 6 7 7 8 9 9 9 9 10] probe duplicates/sole [1 1 2 3 4 4 4 5 6 7 7 8 9 9 9 9 10] ; The output is: ;[1 4 4 7 9 9 9] ;[1 4 7 9]