How to Merge and Sum Values of Shared Keys in Flat Associative Arrays?

Merge and Sum Values in Flat Associative Arrays

Problem:

You have multiple flat associative arrays and want to merge them, adding together the values associated with matching keys without overwriting existing values. The standard array_merge() function, as well as a simple addition operation, do not provide the desired behavior.

Solution:

To merge associative arrays and sum the values of shared keys, you can use one of the following approaches:

1. Loop over the Combined Keys:

<code class="php">$sums = array();
foreach (array_keys($a1 + $a2) as $key) {
    $sums[$key] = (isset($a1[$key]) ? $a1[$key] : 0) + (isset($a2[$key]) ? $a2[$key] : 0);
}</code>

This approach loops through the keys of the combined arrays and accumulates the values for each key into the $sums array.

2. Use Mapping:

<code class="php">$keys = array_fill_keys(array_keys($a1 + $a2), 0);
$sums = array_map(function ($a1, $a2) { return $a1 + $a2; }, array_merge($keys, $a1), array_merge($keys, $a2));</code>

Here, we create an array with all the unique keys from the input arrays and then use array_map() to map a function that sums the values associated with each key in the arrays.

3. Helper Function:

If you frequently need to perform this operation, you can create a helper function:

<code class="php">function array_sum_identical_keys() {
    $arrays = func_get_args();
    $keys = array_keys(array_reduce($arrays, function ($keys, $arr) { return $keys + $arr; }, array()));
    $sums = array();

    foreach ($keys as $key) {
        $sums[$key] = array_reduce($arrays, function ($sum, $arr) use ($key) { return $sum + @$arr[$key]; });
    }
    return $sums;
}</code>

This function accepts any number of arrays and sums the values of shared keys into a new array.

By using one of these approaches, you can merge and sum the values of shared keys in flat associative arrays, resulting in the desired behavior.

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