sub AssembleByHash
{
        my ($array_ref) = @_;
        my (%result);

        foreach my $row (@$array_ref)
        {
                $result{$row->[0]} = $row->[1];
        }

        return \%result;
}

##</code><code>##

sub AssembleByArray
{
        my ($array_ref) = @_;
        my (%result);

        %result = map { @$_ } @$array_ref;

        return \%result;
}

##</code><code>##

Benchmark: timing 10 iterations of AssembleByArray, AssembleByHash...
AssembleByArray: 10 wallclock secs ( 9.64 usr +  0.04 sys =  9.68 CPU) @  1.03/s (n=10)
AssembleByHash:  1 wallclock secs ( 1.31 usr +  0.00 sys =  1.31 CPU) @  7.63/s (n=10)
                  Rate AssembleByArray  AssembleByHash
AssembleByArray 1.03/s              --            -86%
AssembleByHash  7.63/s            639%              --