Determining how 'deep' an element of a multidimensional array is

I need to determine how 'deep' an element is within a multidimensional array. For example, following the code snippet, how can I determine whether an element is in the first level, the second level, the third level, etc.? How can I determine that "Vancouver" is nested three levels deep?

Ideally I would be looking for a return of an integer - so looking for "Countries" would return 0, "USA" would return 1, "Seattle" would return 2, etc.

$myArray = array(
		"Countries" => array(
				"Canada" => array(
						"Vancouver", "Toronto"),
				"USA" => array(
						"New York", "Seattle"),
				     ),
		);

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