@test = (23,23,4,8,21,90,90,90,90,2,2,2,19,21,19);
map {
    $length = ($test[$_ - 1] == $last)? $length + 1: 1;
    $run++ unless  $test[$_ - 1] == $last;
    $last = $test[$_ - 1];
    $runlengths[$run] = [$test[$_ - 1], $length];
} (1 .. scalar @test);