The getValueByKey function used at https://selv.in/blog/traversing-arrays-with-dot-notation

getValueByKey.php

<?php

// @input
$key  = isset($argv[1]) ? $argv[1] : 'name';
$data = array(
	'name'   => 'Brad Bell',
	'mood'   => 'Angry',
	'family' => array(
		'spouse'  => array(
			'name' => 'Brandon Kelly'
		),
		'brother' => array(
			'name' => 'That European Guy'
		)
	)
);

$default = isset($argv[2]) ? $argv[2] : '';

// @usage
echo print_r(getValueByKey($key, $data, $default), true)."\n";

// @process
function getValueByKey($key, array $data, $default = null)
{
	// @assert $key is a non-empty string
	// @assert $data is a loopable array
	// @otherwise return $default value
	if (!is_string($key) || empty($key) || !count($data))
	{
		return $default;
	}

	// @assert $key contains a dot notated string
	if (strpos($key, '.') !== false)
	{
		$keys = explode('.', $key);

		foreach ($keys as $innerKey)
		{
			// @assert $data[$innerKey] is available to continue
			// @otherwise return $default value
			if (!array_key_exists($innerKey, $data))
			{
				return $default;
			}

			$data = $data[$innerKey];
		}

		return $data;
	}

	// @fallback returning value of $key in $data or $default value
	return array_key_exists($key, $data) ? $data[$key] : $default;
}