Merging arrays based on a value of the key

Question

I have two arrays of arrays that have an id key, and I\'d like to merge the data together based on that array\'s key and key value. The data would look somethin

Answer 1

You need to traverse all elements from both arrays one by one and merge any duplicate elements. To do this you need to perform these steps.

1. Glue both arrays together.

    $arr = [
        ['id' => 1, 'color' => 'red'],
        ['id' => 2, 'color' => 'green'],
        ['id' => 3, 'color' => 'blue'],
        ['id' => 1, 'size' => 'SM'],
        ['id' => 2, 'size' => 'XL'],
        ['id' => 4, 'size' => 'LG'],
        ['id' => 3, 'size' => 'MD'],
    ];
   

2. Loop the combined array copying the items into a new array.

3. If the ID has been seen before don't append the row, but merge it with an existing one.

You can achieve all of this with a single foreach loop and array_merge. There is no need for recursive functions or nested loops.

// Loops on merged arrays and copied elements into a new array
foreach(array_merge($color, $size) as $el){
    // If the element with this id is already in new array then add the elements together
    $merged[$el['id']] = ($merged[$el['id']] ?? []) + $el;
}

The only downside is that you lose the original indexes, but it looks from your question that this was not important to you. If you want, you can reindex the array with

$merged = array_values($merged);

Live Demo