How do you flatten multidimensional arrays in PHP into a two-dimensional array with dot notation keys?

Converting Multidimensional Arrays to 2D Arrays with Dot Notation Keys in PHP

Multidimensional arrays in PHP provide a convenient way to organize complex data structures. However, sometimes it may become necessary to flatten a multidimensional array into a two-dimensional array with dot notation keys. This can be achieved using a recursive approach.

Consider the following example:

<code class="php">$myArray = [
    'key1' => 'value1',
    'key2' => [
        'subkey' => 'subkeyval'
    ],
    'key3' => 'value3',
    'key4' => [
        'subkey4' => [
            'subsubkey4' => 'subsubkeyval4',
            'subsubkey5' => 'subsubkeyval5',
        ],
        'subkey5' => 'subkeyval5'
    ]
];</code>

To convert this array into a two-dimensional array with dot notation keys, we can use the following code:

<code class="php">$ritit = new RecursiveIteratorIterator(new RecursiveArrayIterator($myArray));
$result = [];
foreach ($ritit as $leafValue) {
    $keys = [];
    foreach (range(0, $ritit->getDepth()) as $depth) {
        $keys[] = $ritit->getSubIterator($depth)->key();
    }
    $result[join('.', $keys)] = $leafValue;
}</code>

This code iterates recursively over the multidimensional array, using the RecursiveIteratorIterator and RecursiveArrayIterator classes. For each leaf value in the array, it creates a dot notation key by joining the keys of the parent and child arrays. The result is a new two-dimensional array with dot notation keys, as shown below:

<code class="php">[
    'key1' => 'value1',
    'key2.subkey' => 'subkeyval',
    'key3' => 'value3',
    'key4.subkey4.subsubkey4' => 'subsubkeyval4',
    'key4.subkey4.subsubkey5' => 'subsubkeyval5',
    'key4.subkey5' => 'subkeyval5'
]</code>

This technique can be particularly useful when working with data that needs to be converted to a flat structure for processing or display.

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