@property<EOL><INDENT>def per_system_data(self):<DEDENT>
ret = {}<EOL>for cache_date in self.cache_dates:<EOL><INDENT>data = self._cache_get(cache_date)<EOL>ret[cache_date] = {<EOL>self._column_value(x): data['<STR_LIT>'][x]<EOL>for x in data['<STR_LIT>']<EOL>}<EOL>if len(ret[cache_date]) == <NUM_LIT:0>:<EOL><INDENT>ret[cache_date]['<STR_LIT>'] = <NUM_LIT:0><EOL><DEDENT><DEDENT>return ret<EOL>
Return download data by system.

:return: dict of cache data; keys are datetime objects, values are
  dict of system (str) to count (int)
:rtype: dict