Since your dates appear to be in a nice comparable format, you can just do ordinary string comparisons on them to find out which is oldest. So ... something like this should work fine: 

#!/usr/bin/perl

use strict; use warnings;

my (%oldest_date, %oldest_entry);
while (<DATA>)
{
    my ($item,$group,$date) = split;
    if (!exists $oldest_date{$group} || $date lt $oldest_date{$group})
+ {
        $oldest_date{$group} = $date;
        $oldest_entry{$group} = $_;
    }
}

for my $g  (keys %oldest_entry) {
    print $oldest_entry{$g};
}


__DATA__
34     gr1    2003-03-02
12     gr1    1990-03-14
39     gr3    2002-04-11
66     gr4    2006-03-16
32     gr3    1998-02-13
90     gr1    2004-06-15
55     gr4    1999-06-15

[download]

duff

In reply to Re: Pulling out oldest entries from a text file by duff
in thread Pulling out oldest entries from a text file by Angharad

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.