def _select_data(self, x: np.ndarray) -> np.ndarray:
        """
        Select data to attack.

        :param x: An array with the source input to the victim classifier.
        :return: An array with the selected input to the victim classifier.
        """
        nb_stolen = np.minimum(self.nb_stolen, x.shape[0])
        rnd_index = np.random.choice(x.shape[0], nb_stolen, replace=False)

        return x[rnd_index].astype(ART_NUMPY_DTYPE)

        Select data to attack.

        :param x: An array with the source input to the victim classifier.
        :return: An array with the selected input to the victim classifier.
        
art/attacks/extraction/copycat_cnn.py