def is_missing(self):
        """Find missing genotype calls.

        Returns
        -------
        out : ndarray, bool, shape (n_variants, n_samples)
            Array where elements are True if the genotype call matches the
            condition.

        Examples
        --------

        >>> import allel
        >>> g = allel.GenotypeArray([[[0, 0], [0, 1]],
        ...                          [[0, 1], [1, 1]],
        ...                          [[0, 2], [-1, -1]]])
        >>> g.is_missing()
        array([[False, False],
               [False, False],
               [False,  True]])
        >>> v = g[:, 1]
        >>> v
        <GenotypeVector shape=(3, 2) dtype=int64>
        0/1 1/1 ./.
        >>> v.is_missing()
        array([False, False,  True])

        """

        out = np.any(self.values < 0, axis=-1)

        # handle mask
        if self.mask is not None:
            out |= self.mask

        return out
Find missing genotype calls.

        Returns
        -------
        out : ndarray, bool, shape (n_variants, n_samples)
            Array where elements are True if the genotype call matches the
            condition.

        Examples
        --------

        >>> import allel
        >>> g = allel.GenotypeArray([[[0, 0], [0, 1]],
        ...                          [[0, 1], [1, 1]],
        ...                          [[0, 2], [-1, -1]]])
        >>> g.is_missing()
        array([[False, False],
               [False, False],
               [False,  True]])
        >>> v = g[:, 1]
        >>> v
        <GenotypeVector shape=(3, 2) dtype=int64>
        0/1 1/1 ./.
        >>> v.is_missing()
        array([False, False,  True])