[Omaha.pm] Sort quickie

[Jay Hannah]

I had a bunch of hash keys that were dates in MMDDYYYY format. I wanted 
to get a sorted list of the keys. Perl to the rescue! Have y'all 
configured custom sort subroutines before? They're cool...

The real code in context...
------------
    print "\n\nGroup pickup by cap_date (running total):\n";
    foreach (sort sort_by_cap_date keys %{$group_pickup{by_cap_date}}) {
       my $val = $group_pickup{by_cap_date}{$_};
       next if $val == 0;
       print "$_: $val\n";
    }
}

sub sort_by_cap_date ($$) {
    # We have to throw some mojo here since capdate is MMDDYYYY and 
obviously
    # we can't sort until we turn it into YYYYMMDD... -jhannah 6/14/04
    my ($a, $b) = @_;
    for ($a, $b) {
       s/(\d\d)(\d\d)(\d\d\d\d)/$3$1$2/;
    }
    $a <=> $b;
}
---------------

Same idea, distilled out to see the results easier and so you can play 
with it:
---------------
my @dates = qw( 05012003 02012004 11012002 );
print join ", ", sort @dates;
print "\n";
print join ", ", sort by_date @dates;
print "\n";

sub by_date ($$) {
    my ($a, $b) = @_;
    for ($a, $b) {
       s/(\d\d)(\d\d)(\d\d\d\d)/$3$1$2/;
    }
    $a <=> $b;
}
----------------

"sort" just does an ASCII sort, which isn't in date order for MMDDYYYY 
dates. Instead, "sort by_date" does a comparison after converting 
MMDDYYYY into YYYYMMDD, which does sort dates correctly. It doesn't 
munge the real values though.

Neat, huh?

perldoc -f sort

j