sub groups_of_n
{
  my $n = shift;
  return map { [@_[$_*$n..$_*$n+$n-1]] } 0..$#_/$n;
}


use POSIX qw(ceil);

sub groups_of_n
{
  my $n = shift;
  my $m = ceil(@_/$n);
  my @r;
  my $i = 0;
  push(@{$r[$i++%$m]},$_) foreach @_;
  @r;
}