How to Recursively Search for a Key in a Multidimensional Array in PHP?

Recursively Search for a Key in a Multidimensional Array

Problem:

The provided find() method attempts to recursively search for a specific key in an associative array and return the associated value. However, the recursion implementation has an issue.

Solution:

The issue with the original code is related to the recursion. It attempts to return the output of the recursive call directly without handling the case where no match is found at the current level. This can lead to the incorrect return value of "did not find" regardless of whether a match exists deeper in the array.

To rectify this, the following code can be used to handle recursion correctly:

<code class="php">private function find($needle, $haystack) {
    foreach ($haystack as $name => $file) {
        if ($needle == $name) {
            return $file;
        } else if(is_array($file)) { //is folder
            $result = $this->find($needle, $file); //file is the new haystack
            if ($result !== "did not find") {
                return $result;
            }
        }               
    }
    
    return "did not find";
}</code>

This updated function checks if the result of the recursive call is not "did not find," indicating that a match was found at a deeper level. In that case, it returns the found value. Otherwise, it returns the "did not find" value as before.

Alternative Solutions:

In modern PHP versions (5.6 and above), alternative solutions utilizing iterators and/or generators can be more efficient and elegant:

<code class="php">function recursiveFind(array $haystack, $needle)
{
    $iterator  = new RecursiveArrayIterator($haystack);
    $recursive = new RecursiveIteratorIterator(
        $iterator,
        RecursiveIteratorIterator::SELF_FIRST
    );
    foreach ($recursive as $key => $value) {
        if ($key === $needle) {
            return $value;
        }
    }
}</code>

This function uses iterators to efficiently traverse the multidimensional array and find the first matching key.

Additionally, generators can be employed to iterate over all matching elements, not just the first one:

<code class="php">function recursiveFind(array $haystack, $needle)
{
    $iterator  = new RecursiveArrayIterator($haystack);
    $recursive = new RecursiveIteratorIterator(
        $iterator,
        RecursiveIteratorIterator::SELF_FIRST
    );
    foreach ($recursive as $key => $value) {
        if ($key === $needle) {
            yield $value;
        }
    }
}

// Usage
foreach (recursiveFind($haystack, $needle) as $value) {
    // Use `$value` here
}</code>

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