<?php

class Test
{
	public function index( )
	{
		$arr = array( 
			array('a' => 'aap', 'n' => 'noot', 'm' => 'mies'), 
			array('a' => 'ding', 'b' => 'flof', 'c' => 'bips'), 
			array( 'd' => 'do', 'e' => 're', 'c' => 'mi') 
		);
	
		$func = array( $this, '_user_func' );
		
		var_dump($arr);	// BEFORE WALK
		array_walk_recursive($arr, $func);
		var_dump($arr);	// AFTER WALK
	}

	/**
	 *	Does something to a row from an array (notice the reference)
	 */
	private function _user_func( &$rowValue, $rowIndex )
	{
		$rowValue = 'replaced';
	}
}

$test = new Test();
$test->index();