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Code for Selection with Repetitions in Perl



Possible Selections With Repetition.

Imagine being given the opportunity to pick six (6) exercise books from a book-shop having 10 different brands of exercise books - Ben 10, Chelsea F.C., Superman, Tottenham F.C., Indomitables, Manchester City F.C., Spider Man, Power Rangers, Liverpool F.C. and Bat Man exercise books.
If you happen to be a big Power Rangers fan, nothing stops you from selecting all 6 exercise books to be Power Rangers exercise books.
But you can as well decide to pick only 3 Power Rangers exercise books and make up for the other 3 with any other brands of exercise book.



Code for Repetitive Selection in Perl

The algorithm for Selection with Repetition will be a lot similar to that of combination.

  1. Beginning with the first member in the mother set, match it separately with every member - including itself - until the required Selection group-size (r) is reached.
  2. When every possible Selection with this member is exhausted, move to the next member in the mother set and repeat Step I.

This is how our Repetitive Selection code in Perl will work.

Create a new Perl module file;
Call it Selection.pm.
Type out the adjoining Perl code for Selection with Repetition.








Perl Code for Selection.pm Module

package SELECTION;

BEGIN {
    require Exporter;

    # for the sake of standard
    our $VERSION = 2017.10;

    # Inherit from exporter to export functions and variables
    our @ISA = qw(Exporter);

    # Functions and variables to be exported by default
    our @EXPORT_OK = qw(possibleWordCombinations);
}

use warnings;
use strict;

our @words;
our $r; # min length of word
my $i;
my @complete_group; # array of references

# simulate an object construct
sub new {
    my $self = shift;
    
    my $this = {};
    bless $this, $self;
    
    return $this;
}

# point of entry
# returns an array reference of references
sub groupSelection {
    shift;
    my $arg = shift;
    @words = @{$arg};
    $r = shift;
    @complete_group = ();
    $i = 0;
    
    recursiveFillUp([]);
    return \@complete_group;
}

# pick elements recursively
sub recursiveFillUp {
    my $temp = shift;
    my @picked_elements = ();
    my $j = $i;
    while ($j < scalar @words) {
        # dereference 'temp' and save it as an anonymous array reference
        $picked_elements[$j] = [@{$temp}];
        push @{$picked_elements[$j]}, $words[$j];
        # recoil factor
        $i = $j if $i >= scalar @words;
        # satisfied yet?
        if (scalar @{$picked_elements[$j]} == $r) {
            push @complete_group, $picked_elements[$j];
        } elsif (scalar @{$picked_elements[$j]} < $r) {
            recursiveFillUp($picked_elements[$j]);
        }
        $j++;
    }
    if (defined $picked_elements[--$j] && scalar @{$picked_elements[$j]} == $r) {
        $i++; # keep recoil factor straightened out
    }
}

1;

Main Class

#!/usr/bin/perl;

use strict;
use warnings;

use SELECTION;

my @subjects = ("0", "1", "2", "3", "4", "5", "6", "7", "8", "9");
my $r = 9;

# Use the selection module/class
my $pick = SELECTION->new();

# $result receives an array reference of references
my $result = $pick->groupSelection(\@subjects, $r);

print ("[", join(", ", @subjects), "] selection ", $r, ":\n\n");
# for each array reference in a dereferenced '$result'
my $i = 0;
print (++$i, ": ", join(", ", @{$_}), "\n") for @{$result};
print ("\n\nNumber of ways is ", scalar @{$result}, ".");

print "\n\n";



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