def _get_val(row, input_arr):
    """Extract values from array based on index.

    Parameters
    ----------
    row : :obj:`tuple` of length 3
        3-length index into ``input_arr``.
    input_arr : 3D :obj:`numpy.ndarray`
        Array from which to extract value.

    Returns
    -------
    :obj:`float` or :obj:`int`
        The value from ``input_arr`` at the row index.
    """
    i, j, k = row
    return input_arr[i, j, k]