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my %master_hash;

for my $anon_hash_ref ( @AoH ) {
    $master_hash{ $$anon_hash_ref{id} } += $$anon_hash_ref{value};
}

for my $anonhash ( @AoH ) {
    $master_hash{ $$anonhash{id_a} } += $$anonhash{value_x};
    $master_hash{ $$anonhash{id_b} } += $$anonhash{value_y};
}

for my $anonhash ( @AoH ) {
    $master_hash{ "a".$$anonhash{id_a} } += $$anonhash{value_x};
    $master_hash{ "b".$$anonhash{id_b} } += $$anonhash{value_y};
}

for my $anonhash ( @AoH ) {
    my $newkey = join '_', 'a', $$anonhash{id_a}, 'b', $$anonhash{id_b
+};
...
    $master_hash{$newkey}[0] += $$anonhash{value_x};
    $master_hash{$newkey}[1] += $$anonhash{value_y};
}