# P08 - Eliminate consecutive duplicates of list elements.

*Author: Johan Viklund*

We define an infix operator called 'compress' such that:

'a' compress 'a' gives 'a' 'a' compress 'b' gives ('a','b')

(@a,'a') compress 'a' gives ( @a,'a') (@a,'a') compress 'b' gives ( @a,'a','b')

Now all we need to do is split our array up and insert compress.

given <a a b c c d> we want: 'a' compress 'a' compress 'b' compress 'c' compress 'c' compress 'd'

The reduce metaoperator does exactly this. For example:

[+] (1,2,3,4,5) == 1 + 2 + 3 + 4 + 5 == 15 [~] <a b c d e> eq 'a' ~ 'b' ~ 'c' ~ 'd' ~ 'e' eq 'abcde'

# Specification

P08 (**) Eliminate consecutive duplicates of list elements. If a list contains repeated elements they should be replaced with a single copy of the element. The order of the elements should not be changed.

# Example

> say [compress] <a a a a b c c a a d e e e e> a b c a d e

Source code: P08-viklund.pl

use v6; multi infix:<compress> ( $a, $b ) { $a ~~ $b ?? $a !! ( $a, $b ) } multi infix:<compress> ( @a, $b ) { @a[*-1] ~~ $b ?? @a !! ( @a, $b ).flat } say ([compress] <a a a a b c c a a d e e e e>).perl;