#!/usr/bin/perl -w
use strict;

my $entries;

while ( my $line = <DATA> ){
		$line =~ /\d?\W*(gr\d)\W*(\d*-\d\d-\d\d)/;
		next if ( !$2 );

		my $group = $1;
		my $date = $2;
		$date =~ s/-//g;

		if ( ! defined( $entries->{$group})   || 
				( $entries->{$group}->{date} < $date )  ){
				$entries->{$group}->{date} = $date;
				$entries->{$group}->{entry} = $line;
		}

}

foreach (keys( %{$entries} )){
		print "entry: $entries->{$_}->{entry}";
}




__DATA__
item  group  entry_date
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
etc ...

##</code><code>##

#!/usr/bin/perl -w


open F, ">testdata";



for ( 0..1000000 ){
		print F "$_  gr".int(rand(10))."  ". (1990+int(rand(25))) . '-0'. (int(rand(10))) . '-' . (10 + int(rand(20)) )."\n";
}
close F;

##</code><code>##

my code:

time ./latestentries.pl
entry: 15970  gr5  2014-09-29
entry: 79485  gr8  2014-09-29
entry: 135788  gr7  2014-09-29
entry: 221  gr2  2014-09-29
entry: 18669  gr9  2014-09-29
entry: 46760  gr1  2014-09-29
entry: 4960  gr3  2014-09-29
entry: 9486  gr0  2014-09-29
entry: 19710  gr4  2014-09-29
entry: 56757  gr6  2014-09-29

real    0m8.689s
user    0m8.617s
sys     0m0.060s

-------------------
anno's code:

micha@laptop ~/prog/perl/test $ time perl test-anno.pl
962757, gr0, 2014-09-29
964472, gr1, 2014-09-29
984704, gr2, 2014-09-29
980128, gr3, 2014-09-29
985851, gr4, 2014-09-29
931318, gr5, 2014-09-29
976880, gr6, 2014-09-29
988367, gr7, 2014-09-29
992654, gr8, 2014-09-29
962175, gr9, 2014-09-29

real    0m4.556s
user    0m4.424s
sys     0m0.036s

-------------------
and duff's entry:

micha@laptop ~/prog/perl/test $ time perl test-duff.pl
100154  gr5  1990-00-10
5654  gr8  1990-00-10
2318  gr7  1990-00-10
9789  gr2  1990-00-10
19151  gr9  1990-00-10
91314  gr1  1990-00-10
124846  gr3  1990-00-10
14858  gr0  1990-00-10
175946  gr4  1990-00-10
95691  gr6  1990-00-10

real    0m3.497s
user    0m3.452s
sys     0m0.036s