#!/usr/bin/env perl

use strict;
use warnings;

my %data = qw{a 1 b 2 c 3 d 4 e 5 f 6 g 7 h 8 i 9};
my $N = $ARGV[0];
my $i = 0;
my %work; 
$work{(($i += 1) % $N) + 1}{$_} = $data{$_} for keys %data;

use Data::Dump;
dd \%work;