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I mostly wrote the following as a tutorial to myself as to how Perl's sorting function works:
#!/usr/bin/perl -w use strict; #simple sort tests my @a; @a = (3,5,9,2,15,90,200); print "Standard sort: " , join(" ",sort(@a)); print "\nCorreted numeric sort: ", join(" ", sort {$a <=> $b} @a); #try dates my @b = ('11/5/99','2/5/87','11/6/99'); print "\nUnsorted Dates: " , join(" ", @b) , "\n"; print "\nCustom Date Sort: ", join(" ", sort {date_sort($a, $b)} @b); sub date_sort { my ($first, $second) = @_; if($first =~ m/(\d+)\/(\d+)\/(\d+)/g) { my (@mm, @dd, @yy); ($mm[1], $dd[1], $yy[1]) = ($1, $2, $3); if ($yy[1] > 50) {$yy[1] += 1900} else {$yy[1] += 2000}; if($second =~ m/(\d+)\/(\d+)\/(\d+)/g) { ($mm[2], $dd[2], $yy[2]) = ($1, $2, $3); } if ($yy[2] > 50) {$yy[2] += 1900} else {$yy[2] += 2000}; if ($yy[1] > $yy[2]) {return($first cmp $second)} elsif ($yy[1] < $yy[2]) {return($second cmp $first)} else { #fall into testing month dates if($mm[1] > $mm[2]) {return ($first cmp $second)} elsif($mm[2] > $mm[1]) {return ($second cmp $first)} else { #if that fails, test the days if($dd[1] > $dd[2]) {return ($first cmp $second)} else {return ($second cmp $first)} } } ; } } 1;
Quick explanation

The first and second sorts use Perl's standard sorting syntax. Nothing special here.

Perl also allows you to call a special sorting routine sort {date_sort($a, $b)} @b where the stuff between the curly braces is your call to the special function. The function basically checks the date and returns either one of two options...either $a is greater than $b or the reverse.

This is a very involved way to sort some bloody dates but, if you think about it, you could reuse the code if you needed a very, very specialized kind of date comparison function...e.g. perhaps something that seeks a particular range of dates and places them at the top of the sort order or something.

Oops...I tried a different set for the test data for this function and I am getting incorrect results. Don't use this for dates < 1950. Celebrate Intellectual Diversity


In reply to Re: sorting mm/dd/yy by InfiniteSilence
in thread sorting mm/dd/yy by electronicMacks

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