#! /usr/bin/perl
use strict;
use warnings;


my %words = qw(
    als 5
    wie 3
    Von 3
    zu  5
    von 10
);

my %by_number;

while ( my ($k,$v) = each %words ) {
    push @{ $by_number{$v} }, $k;
}


require Data::Dumper;
print Data::Dumper->new( [ \%by_number ], [ qw( *by_number ) ] )->Sortkeys(1)->Dump();