Here is a way to get the difference between the dates in days from an array of dates. (Note that the dates are sorted. If your array isn't sorted you would have some negative differences). 
#!/usr/bin/perl
use strict;
use warnings;
use Time::Piece;


my @date = (
    '2014-06-01',
    '2014-06-02',
    '2014-06-03',
    '2014-06-04'
);

for my $i (0 .. $#date-1) {
    my $d1 = Time::Piece->strptime($date[$i], '%Y-%m-%d');
    for my $j ($i+1 .. $#date) {
        my $d2 = Time::Piece->strptime($date[$j], '%Y-%m-%d');
        my $diff = $d2 - $d1;
        print $d1->ymd, " and ", $d2->ymd, " is ", $diff->days, "\n";
    }    
}

[download]
Prints 
2014-06-01 and 2014-06-02 is 1
2014-06-01 and 2014-06-03 is 2
2014-06-01 and 2014-06-04 is 3
2014-06-02 and 2014-06-03 is 1
2014-06-02 and 2014-06-04 is 2
2014-06-03 and 2014-06-04 is 1

[download]

In reply to Re^3: Hash Math by Cristoforo
in thread Hash Math by marlowvoltron

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