use strict;
use warnings;
use 5.010;

my $data =<<"END_OF_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
END_OF_DATA

say $data;

--output:--
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


my @lines;

#OPEN YOUR FILE HERE:

open my $INFILE, '<', \$data
    or die "Couldn't open string for reading: $!";

#What I did was I opened the string $data as if it were a file.
#Now I can treat $INFILE as if it were a file...

for my $line (<$INFILE>) {
    chomp $line;

    if($line) {
        push @lines, [split ' ', $line];
    }
}

use Data::Dumper;
say Dumper(\@lines);

--output:--
$VAR1 = [
          [
            '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'
          ]
        ];




my @sorted = sort{ $a->[1] <=> $b->[1]
                or $a->[0] <=> $b->[0]}
             @lines;

say Dumper(\@sorted);

--output:--
$VAR1 = [
          [
            '1.000',
            '32.051',
            '2840.0'
          ],
          [
            '1.050',
            '32.051',
            '3280.0'
          ],
          [
            '1.100',
            '32.051',
            '3720.0'
          ],
          [
            '1.000',
            '42.735',
            '2840.0'
          ],
          [
            '1.050',
            '42.735',
            '3280.0'
          ],
          [
            '1.100',
            '42.735',
            '3720.0'
          ],
          [
            '1.000',
            '64.103',
            '2840.0'
          ],
          [
            '1.050',
            '64.103',
            '3280.0'
          ],
          [
            '1.100',
            '64.103',
            '3720.0'
          ]
        ];


my @results = map {my @arr = @$_;
                   join ' ', @arr}
              @sorted;

say Dumper(\@results);

--output:--
$VAR1 = [
          '1.000 32.051 2840.0',
          '1.050 32.051 3280.0',
          '1.100 32.051 3720.0',
          '1.000 42.735 2840.0',
          '1.050 42.735 3280.0',
          '1.100 42.735 3720.0',
          '1.000 64.103 2840.0',
          '1.050 64.103 3280.0',
          '1.100 64.103 3720.0'
        ];



for (@results) {
  say;
}

--output:--
1.000 32.051 2840.0
1.050 32.051 3280.0
1.100 32.051 3720.0
1.000 42.735 2840.0
1.050 42.735 3280.0
1.100 42.735 3720.0
1.000 64.103 2840.0
1.050 64.103 3280.0
1.100 64.103 3720.0