Having had bad experience with Text::CSV_XS (I'm guessing it was probably me, not the module ;o) I tend to use hand-rolled solutions if it's nice'n'simple (I mean *really* simple), otherwise it's best to rely on the tried-and-tested APIs available. So anyway here's my meagre effort -

use strict;

$_ = <DATA>;
my $cnt = tr/,/,/ + 1;

my @fields;
push @fields, split /,/ while <DATA>;
chomp(@fields);

my %data;
push @{$data{$_ % $cnt}}, $fields[$_] for 0..@fields-1;

my @row;
for (keys %data) {
        @row = sort @{$data{$_}};
        print "$_ - @row\n";
}

__END__
num1,num2,num3
123,345,578
345,349,340
12,348,023
534,90283,230
239,394,283
[download]

What this does is

• counts the amount of fields (which in turn assumes theres a header line)
• stores all the data in a flat array
• get's rid of those danged newlines
• creates a hash with the columns as the keys
• then just loops through the data and sorts each column

Sorry if this is a little direct in approach, but if you're rolling your own it might nudge you in the right direction (and I was looking for a challenge, simple though it is :o)
HTH

broquaint

Update: it's probably best to go with davorg's approach if you actually want to implement this, but I'll leave this here in the spirit of TMTOWTDI.

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