Question

I have two arrays that look like this:

(this one is ordered by value_max)

$max_values = [
    ["name" => "john", "id" => 5, "value_max" => 500], 
    ["name" => "john", "id" => 3, "value_max" => 200], 
    ...
];

$min_values = [
    ["name" => "john", "id" => 5, "value_min" => 100], 
    ["name" => "john", "id" => 3, "value_min" => 150], 
    ...
];

And I need to have a final array like this:

(This one stills need to be ordered by value_max, so I assume I could just overwrite the first array with the calculations done with the second)

$max_and_difference_values = [
    ["name" => "john", "id" => 5, "value_max" => 500, "difference_value" => 400],
    ["name" => "john", "id" => 3, "value_max" => 200, "difference_value" => 50 ], 
    ...
];

My question is pretty straight: What is the best/effective way to run through both first arrays and build the last one. Assuming that the size of the arrays can be of around 150 elements.

Answer 1

To avoid looping through all arrays repeatedly, index one array by the field you want to merge on, i.e. the 'id' key:

$second = array_combine(array_map(function ($i) { return $i['id']; }, $second_array), $second_array);

Then looping through the other and comparing the values is pretty easy:

$third = array();
foreach ($first_array as $i) {
    $third[] = $i + array('difference_value' => $i['value_max'] - $second[$i['id']]['value_min']);
}

If it’s guaranteed that both arrays will have exactly matching keys, you don’t even need the first step and just go by already existing keys.