use strict;
use warnings;

my @lines = <DATA>;

@lines = map {[/(\d+\.\d+)/g]} @lines;
@lines = sort {$a->[1] <=> $b->[1] or $a->[0] <=> $b->[0]} @lines;

print "@$_\n" for @lines;

__DATA__
48.1 0.4 99.0 0.5
1.0 0.2 99.0 0.3
1.0 0.1 99.0 0.2
1.0 0.3 99.0 0.4
1.0 0.5 99.0 0.6
13.1 0.6 99.0 0.7
5.0 0.4 48.0 0.5
1.0 0.6 13.0 0.7