public function walk(Closure $callback) {
		foreach($this->_data as &$data) {
			$data = $callback($data);
		}
		unset($data);
		
		return $this;
	}
public function walk(Closure $callback) {
		foreach($this->_data as &$data) {
			$data = $callback($data);
		}
		unset($data);
		
		return $this;
	}
public function walk ( Closure $ callback ) { foreach ( $ this -> _data as & $ data ) { $ data = $ callback ( $ data ) ; } unset ( $ data ) ; return $ this ; }
Processing a collection's data

@param  Closure $callback callback
@return Collection
Processing a collection s data