Nested array creation

array_nested_create.php

<?php

$taxes = [
    [
        'country_id' => 'a',
        'value' => 42,
        'type' => 't1',
    ],
    [
        'country_id' => 'a',
        'value' => 88,
        'type' => 't2',
    ],
    [
        'country_id' => 'b',
        'value' => 10,
        'type' => 't1',
    ],
];

$countries = [
    [
        'id' => 'a',
        'code' => 'a_code',
    ],
    [
        'id' => 'b',
        'code' => 'b_code',
    ],
    [
        'id' => 'c',
        'code' => 'c_code',
    ],
];

$countryTaxMap = [
    'd_code' => [
        't4' => 8,
    ],
];

foreach ($taxes as $tax) {
    foreach ($countries as $country) {
        if ($tax['country_id'] == $country['id']) {
            $countryTaxMap[$country['code']][$tax['type']] = $tax['value'];
        }
    }
}

print_r($countryTaxMap);

echo PHP_EOL;