Hi Anonymous Monk

I recommend you to have a look at the following nodes for information on PDL

• RFC: Getting Started with PDL (the Perl Data Language)
• The Perl Data Language (PDL): A Quick Reference Guide
• RFC: PDL Cheat Sheet

Now, answering your question, you could use the function minimum together with xchg as in the following example:

#!/usr/bin/perl
use warnings;
use strict;

use PDL;
my ( @data, @tmp );
while (defined(my $line = <DATA>)) {
    chomp ($line);
    @tmp = split /\s+/, $line;
    push @data, [ @tmp ];
}

my $patterns = pdl(@data);

my $minimum = minimum($patterns->xchg(0,1));
print "minimum: $minimum\n";

__DATA__
2.0    4.0
4.0    5.0
5.0    4.0
5.5    6.0
5.0    5.0
4.5    4.5
5.0    5.5
5.5    5.0
5.0    4.5
4.5    5.0
9.5    -1.0
9.0    9.5
8.0    8.0
7.0    8.0
8.0    7.0
8.5    7.0
7.0    8.5
7.0    7.0
7.5    7.0
6.5    8.0
8.0    6.5
6.5    7.0
10.0    10.0
10.0    9.0
10.0    9.0
9.5    10.0
8.0    10.0
9.5    9.5
9.0    9.0
9.0    10.0
[download]

The output is:

minimum: [2 -1]
[download]

Cheers,