def get_hazard(self, data=None):
        """
        :param data: if given, an iterator of records of dtype gmf_dt
        :returns: sid -> records
        """
        if data is None:
            data = self.get_gmfdata()
        return general.group_array(data, 'sid')
:param data: if given, an iterator of records of dtype gmf_dt
        :returns: sid -> records