DeepArray to simplifies work with arbitrarily deeply nested arrays.

DeepArray.php

<?php

/**
 * Simplifies work with deep nested arrays.
 *
 * @author Tomasz Darmetko <tomasz.darmetko@gmail.com>
 */
class DeepArray
{

    /**
     * Set an value in nested array.
     *
     * @param array $array Nested array where value will be set
     * @param array $keys  Keys pointing to the place where new value must be set
     * @param mixed $value The value to set
     */
    static public function set(array &$array, array $keys, $value)
    {
        $reference =& static::getReference($array, $keys);
        /** @noinspection SuspiciousAssignmentsInspection */
        $reference = $value;
    }

    /**
     * Get an value from the nested array.
     *
     * @param array      $array   Nested array whose value will be returned
     * @param array      $keys    Keys pointing to the value
     * @param mixed|null $default Default value to return if no value have been found
     *
     * @return mixed Value found in the array or default value
     */
    static public function get(array $array, array $keys, $default = null)
    {
        // PHP does not have a syntax to dynamically access arbitrary nested arrays
        // use a simple loop to do this programmatically
        $value =& $array;
        foreach ($keys as $key) {
            // check if combination contains any value
            if (isset($value[$key]) || array_key_exists($key, $value)) {
                // use a reference as a simple trick to not create new arrays over and over
                $value =& $value[$key];
            } else {
                return $default; // array does not contain one of the keys, return default value
            }
        }

        return $value;
    }

    /**
     * Returns reference to the value on specified position in the array.
     *
     * @param array      $array   Nested array to whose value an reference will be returned
     * @param array      $keys    Keys pointing to the value
     * @param mixed|null $default Default value to set if no value have been found
     *
     * @return mixed Reference to the value on specified position in the array.
     */
    static public function &getReference(array &$array, array $keys, $default = null)
    {
        // spacial case when no keys are given
        if (empty($keys)) {
            $array = $default;

            return $array;
        }

        // pop last key from given keys, if the key does not exists in the stored array
        // the default value must be set for this key instead of standard empty array as in the loop below
        $lastKey = array_pop($keys);

        // go trough all nested arrays (without the deepest reference, this array will contain the value)
        foreach ($keys as $key) {

            // check if nested array exists, create one if not
            if (!isset($array[$key])) {
                $array[$key] = [];
            }

            // get a reference to the next nested array
            $array =& $array[$key];

        }

        // check if value was found, set the default value if not
        if (!array_key_exists($lastKey, $array)) {
            $array[$lastKey] = $default;
        }

        // return reference to the value
        return $array[$lastKey];
    }

    /**
     * Recursive walk trough given array on required level.
     * This function will recurse into structure of the array up to specified level and invoke given callable with two
     * parameters. The first parameter are keys of nested arrays and the second is value stored in the arrays on
     * specified level.
     *
     * @param array    $array    Array to walk trough
     * @param int      $level    Level on which array must be walked trough
     * @param callable $callable Signature of callable, function(array $keys, $value) : void
     * @param array    $keys     @internal Allows to remember keys of nested arrays up to required level
     */
    static public function recursiveWalkForLevel(array &$array, int $level, callable $callable, $keys = [])
    {
        if ($level > 1) {
            foreach ($array as $key => &$nestedArray) {
                $currentKeys = $keys;
                $currentKeys[] = $key;
                static::recursiveWalkForLevel($nestedArray, $level - 1, $callable, $currentKeys);
            }
        } else {
            foreach ($array as $key => &$value) {
                $currentKeys = $keys;
                $currentKeys[] = $key;
                $callable($currentKeys, $value);
            }
        }
    }

    /**
     * Creates recursive iterator that iterates trough given array on required level. Iterator will recurse into
     * structure of the array up to specified level. Iterator for each value of the array will provide as a key an
     * array consisting of keys of nested arrays leading to the value.
     *
     * Warning! Iterator on deeply nested arrays is around 2 times slower than walking trough the array. Although it is
     * marginally faster tough on flat arrays. @see DeepArrayBench
     *
     * @param array $array      Array to iterate on
     * @param int   $level      Level on which array must be iterated on
     * @param bool  $revertKeys @internal Allows to revert order of keys passed as a key for value during iteration
     *
     * @return \Generator
     */
    static public function createIteratorForLevel(array $array, int $level, $revertKeys = true): \Generator
    {
        if ($level > 1) {
            foreach ($array as $key => $nestedArray) {
                foreach (self::createIteratorForLevel($nestedArray, $level - 1, false) as $keys => $value) {

                    $keys[] = $key;

                    if ($revertKeys) {
                        $keys = array_reverse($keys);
                    }

                    yield $keys => $value;

                }
            }
        } else {
            foreach ($array as $key => $value) {
                yield [$key] => $value;
            }
        }
    }

}