Check if the input is an SArray. Provide a proper error
    message otherwise.

def _raise_error_if_not_sarray(dataset, variable_name="SArray"):
    """
    Check if the input is an SArray. Provide a proper error
    message otherwise.
    """
    err_msg = "Input %s is not an SArray."
    if not isinstance(dataset, _SArray):
      raise ToolkitError(err_msg % variable_name)