List Splitter / Unmerge List

[CharlesClarkson]

This routine splits a list into more than one list.

my @arr = qw ( apples oranges bananas pears berries apricots   );
my @arr_of_columns = split_list( \@arr, 2 );

giving us:

    ['apples', 'bananas','berries', 'prunes']
    ['oranges','pears',  'apricots']

If you want to pad the end of uneven arrays place the padding as the third argument

my $arr_of_arr = split_list( [ 1 .. 7 ], 3, undef ); which gives:

    [1,4,7]
    [2,5,undef]
    [3,6,undef]

A note of caution: The original array is left intact. If split_list is used on large arrays you could run out of memory before this task completes.

Update:Changed title to mention unmerge. Thanks, belg4mit

sub split_list {
    use integer;
    my ( $list_ref, $qty, $pad ) = @_;
    return unless ref $list_ref eq 'ARRAY';
    my @return;
    if ( !( @$list_ref % $qty ) || @_ == 2  ) {
        push @{ $return[$_ % $qty] }, $list_ref->[$_] for 0 .. $#$list
+_ref;

    } else {
        my $padded = $qty - @$list_ref % $qty;
        push @{ $list_ref }, ($pad) x $padded;
        push @{ $return[$_ % $qty] }, $list_ref->[$_] for 0 .. $#$list
+_ref;
        pop @$list_ref for 1 .. $padded;
    }
    return @return if wantarray;
    return \@return;
}

[belg4mit]

IIRC the conventional name for this is unmerge. At least that's what the RFC used. Also the use of split in the name is a bit confusing here as I would have expected such a thing to give:

([qw(apples oranges bananas)],
 [qw(pears berries apricots)]);

I could also see zip and unzip being used (to highlight the interlacing).

--
perl -pe "s/\b;([st])/'\1/mg"