def _filter(self) -> None:
        """Filter MNIST dataset: select images of 0, 1, 2, 3, 4 classes."""
        mask = self.targets < self._split
        self.data = self.data[mask]
        self.targets = self.targets[mask]
Filter MNIST dataset: select images of 0, 1, 2, 3, 4 classes.
catalyst/contrib/datasets/mnist.py