def compute_number_of_masked_points(data_array):
    """Count number of '1' in the data array.

    Args:
        data_array (vtkIntArray): Array to check.

    Returns:
        number_of_points (int): Number of '1' in array.
    """
    number_of_points = 0
    for i in range(data_array.GetNumberOfTuples()):
        value = data_array.GetTuple1(i)
        if value == 1:
            number_of_points += 1

    return number_of_points