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

my @x = map {$_->[0]}
       sort {$b->[2] <=> $a->[2] ||
             $a->[1] <=> $b->[1] }
        map {[$_, split]} grep {/\S/} <DATA>;

for my $i (0 .. $#x) {
    print $x[$i];
    print "\n" if ($i + 1) % 3 == 0;
}
__DATA__
1.000    64.103    2840.0
1.000    42.735    2840.0
1.000    32.051    2840.0

1.050    64.103    3280.0
1.050    42.735    3280.0
1.050    32.051    3280.0

1.100    64.103    3720.0
1.100    42.735    3720.0
1.100    32.051    3720.0
[download]

prints

1.000   64.103  2840.0
1.050   64.103  3280.0
1.100   64.103  3720.0

1.000   42.735  2840.0
1.050   42.735  3280.0
1.100   42.735  3720.0

1.000   32.051  2840.0
1.050   32.051  3280.0
1.100   32.051  3720.0
[download]