$i = -1;
while (<FILE>){  
    chomp;
    $i++;
   ($last[$i], $first[$i], $age[$i], $sex[$i], $height[$i], $weight[$i]) = split/,/;
}
die "Sorry, no data\n" if $i == -1;

##</code><code>##

@alphabetical = sort @alphabetical

# the above is equivalent to
@alphabetical = sort {$a cmp $b} @alphabetical

@numerical = sort {$a <=> $b} @numerical;

# to reverse the sort order reverse the positions of $a and $b, or use reverse sort @a