Combine elements within the array

Question

I have no idea why this question has been marked as a duplicate, because the so-called duplicate is about using array_merge to combine arrays - this question is about combining element trees WITHIN an array.

Is there a way to combine individual elements and their subtrees within a PHP array? For instance, to convert this:

$test = array(
    "EW" => array(313, 1788),
    "SC" => array(670, 860),
    "FR" => array(704, 709),
    "UK" => array(423, 1733)
);

into this:

$test1 = array(
    "UK" => array(313, 423, 670, 860, 1733, 1788),
    "FR" => array(704, 709)
);

where the entries for EW and SC have been combined with those for UK.

array_combine and array_merge seem to work between arrays, not within them, so I'm not clear how to approach this.

Answer 1

You'll have to make a map of keys that have to be grouped with another key ($group_keys in the code below)

$test= [
    'EW' => [313, 1788], 
    'SC' => [670, 860], 
    'FR' => [704, 709], 
    'UK' => [423, 1733]
];

$group_keys=[
    'EW' => 'UK', 
    'SC' => 'UK'
];

$result = [];
foreach($test as $code => $values) {
    if (isset($group_keys[$code])) {
        $target = $group_keys[$code];
    }
    else {
        $target = $code;
    }
    if (isset($result[$target])) {
        $result[$target] = array_merge($result[$target], $values);
    }
    else {
        $result[$target] = $values;
    }
}

print_r($result);

Output:

Array
(
    [UK] => Array
        (
            [0] => 313
            [1] => 1788
            [2] => 670
            [3] => 860
            [4] => 423
            [5] => 1733
        )

    [FR] => Array
        (
            [0] => 704
            [1] => 709
        )

)