use strict;
use warnings;

my %hash=(
    1=> [1.5, 2.1, 3.1],
    2=> [1.2, 2.2, 3.2],
    3=> [1.3, 2.3, 3.3],
    );

my @array = sort {$a<=> $b} map {@{$hash{$_}}} keys %hash;

print "@array";
[download]

Prints:

1.2 1.3 1.5 2.1 2.2 2.3 3.1 3.2 3.3
[download]