my @sorted_aoh =
map $aoh[ substr $_, 5 ],
sort
map {
    # Retrieve the document number
    my $doc_key = (map /^doc(\d+)$/ ? 0 + $1 : (), keys %{$aoh[$_]})[0];

    # Return the document number, a null and the original array index
    pack( 'N', $doc_key ) . "\0" . $_;
} 0 .. $#aoh