use v5.12;
use warnings;
use Data::Dumper;
BEGIN { $ENV{LIST_MOREUTILS_PP} = 1 }; # enforce PP version, comment for XS
use List::MoreUtils qw/slide/;

my @x= split',', q(a,a,a,a,b,c,c,a,a,d,e,e,e,e);

print Dumper slide { $a ne $b ? $b : () } "", @x;