def _expand(self, data):
        # expanding three dimension data to one dimension list
        data_expanded = []
        for i in range(len(data)):
            shapes = np.shape(data[i])
            data_listed = data[i].reshape(1, shapes[0] * shapes[1])
            data_listed = data_listed.getA().tolist()[0]
            data_expanded.extend(data_listed)
        data_expanded = np.asarray(data_expanded)
        return data_expanded