Hi Julien,

I've been testing group by functionality and I found some issues, I'm getting repeated groups with different measures. For example: the group {'project_id': '62e08edf-df81-4898-8ae7-0568fe8be307', 'flavor_id': '572cdbb9-a21e-40d6-a1ce-abca972609df'} has different measures values.

"POST /v1/aggregation/resource/instance/metric/instance?start=2016-01-01T00:00:00&needed_overlap=0.0&granularity=86400&stop=2016-02-01T00:00:00&aggregation=sum&groupby=project_id&groupby=flavor_id HTTP/1.1" 200 6208
RESP: [200] date: Fri, 19 Feb 2016 18:15:35 GMT content-length: 6208 content-type: application/json; charset=UTF-8 server: Apache/2.4.7 (Ubuntu) 
RESP BODY: [{"measures": [], "group": {"project_id": "a046890d-6238-462f-9256-041f003cc06f", "flavor_id": "572cdbb9-a21e-40d6-a1ce-abca972609df"}}, {"measures": [], "group": {"project_id": "8ce5d514-2baf-4dc5-8cf2-8c07ca9e9af9", "flavor_id": "843716b8-1c7a-4522-83f2-836b80a3f11d"}}, {"measures": [], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "572cdbb9-a21e-40d6-a1ce-abca972609df"}}, {"measures": [], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "82e2154f-7816-4844-97b5-10523e488650"}}, {"measures": [], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "572cdbb9-a21e-40d6-a1ce-abca972609df"}}, {"measures": [["2016-01-01T00:00:00+00:00", 86400.0, 1.0], ["2016-01-02T00:00:00+00:00", 86400.0, 1.0], ["2016-01-03T00:00:00+00:00", 86400.0, 1.0], ["2016-01-04T00:00:00+00:00", 86400.0, 1.0], ["2016-01-05T00:00:00+00:00", 86400.0, 1.0], ["2016-01-06T00:00:00+00:00", 86400.0, 1.0], ["2016-01-07T00:00:00+00:00", 86400.0, 1.0], ["2016-01-08T00:00:00+00:00", 86400.0, 1.0], ["2016-01-09T00:00:00+00:00", 86400.0, 1.0], ["2016-01-10T00:00:00+00:00", 86400.0, 1.0], ["2016-01-11T00:00:00+00:00", 86400.0, 1.0], ["2016-01-12T00:00:00+00:00", 86400.0, 1.0], ["2016-01-13T00:00:00+00:00", 86400.0, 1.0], ["2016-01-21T00:00:00+00:00", 86400.0, 1.0], ["2016-01-22T00:00:00+00:00", 86400.0, 1.0], ["2016-01-28T00:00:00+00:00", 86400.0, 1.0]], "group": {"project_id": "8ce5d514-2baf-4dc5-8cf2-8c07ca9e9af9", "flavor_id": "843716b8-1c7a-4522-83f2-836b80a3f11d"}}, {"measures": [["2016-01-01T00:00:00+00:00", 86400.0, 1.0], ["2016-01-02T00:00:00+00:00", 86400.0, 1.0], ["2016-01-03T00:00:00+00:00", 86400.0, 1.0], ["2016-01-04T00:00:00+00:00", 86400.0, 1.0], ["2016-01-05T00:00:00+00:00", 86400.0, 1.0], ["2016-01-06T00:00:00+00:00", 86400.0, 1.0], ["2016-01-07T00:00:00+00:00", 86400.0, 1.0], ["2016-01-08T00:00:00+00:00", 86400.0, 1.0], ["2016-01-09T00:00:00+00:00", 86400.0, 1.0], ["2016-01-10T00:00:00+00:00", 86400.0, 1.0], ["2016-01-11T00:00:00+00:00", 86400.0, 1.0], ["2016-01-12T00:00:00+00:00", 86400.0, 1.0], ["2016-01-13T00:00:00+00:00", 86400.0, 1.0], ["2016-01-21T00:00:00+00:00", 86400.0, 1.0], ["2016-01-22T00:00:00+00:00", 86400.0, 1.0], ["2016-01-28T00:00:00+00:00", 86400.0, 1.0]], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "572cdbb9-a21e-40d6-a1ce-abca972609df"}}, {"measures": [], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "82e2154f-7816-4844-97b5-10523e488650"}}, {"measures": [["2016-01-01T00:00:00+00:00", 86400.0, 1.0], ["2016-01-02T00:00:00+00:00", 86400.0, 1.0], ["2016-01-03T00:00:00+00:00", 86400.0, 1.0], ["2016-01-04T00:00:00+00:00", 86400.0, 1.0], ["2016-01-05T00:00:00+00:00", 86400.0, 1.0], ["2016-01-06T00:00:00+00:00", 86400.0, 1.0], ["2016-01-07T00:00:00+00:00", 86400.0, 1.0], ["2016-01-08T00:00:00+00:00", 86400.0, 1.0], ["2016-01-09T00:00:00+00:00", 86400.0, 1.0], ["2016-01-10T00:00:00+00:00", 86400.0, 1.0], ["2016-01-11T00:00:00+00:00", 86400.0, 1.0], ["2016-01-12T00:00:00+00:00", 86400.0, 1.0], ["2016-01-13T00:00:00+00:00", 86400.0, 1.0], ["2016-01-21T00:00:00+00:00", 86400.0, 1.0], ["2016-01-22T00:00:00+00:00", 86400.0, 1.0], ["2016-01-28T00:00:00+00:00", 86400.0, 1.0]], "group": {"project_id": "8ce5d514-2baf-4dc5-8cf2-8c07ca9e9af9", "flavor_id": "843716b8-1c7a-4522-83f2-836b80a3f11d"}}, {"measures": [["2016-01-01T00:00:00+00:00", 86400.0, 965.0], ["2016-01-02T00:00:00+00:00", 86400.0, 1421.0], ["2016-01-03T00:00:00+00:00", 86400.0, 1434.0], ["2016-01-04T00:00:00+00:00", 86400.0, 1437.0], ["2016-01-05T00:00:00+00:00", 86400.0, 1440.0], ["2016-01-06T00:00:00+00:00", 86400.0, 1396.0], ["2016-01-07T00:00:00+00:00", 86400.0, 1347.0], ["2016-01-08T00:00:00+00:00", 86400.0, 557.0]], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "572cdbb9-a21e-40d6-a1ce-abca972609df"}}, {"measures": [["2016-01-01T00:00:00+00:00", 86400.0, 965.0], ["2016-01-02T00:00:00+00:00", 86400.0, 1421.0], ["2016-01-03T00:00:00+00:00", 86400.0, 1434.0], ["2016-01-04T00:00:00+00:00", 86400.0, 1437.0], ["2016-01-05T00:00:00+00:00", 86400.0, 1440.0], ["2016-01-06T00:00:00+00:00", 86400.0, 1396.0], ["2016-01-07T00:00:00+00:00", 86400.0, 1347.0], ["2016-01-08T00:00:00+00:00", 86400.0, 557.0]], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "34126752-34f2-43ce-8722-86963075fdc9"}}, {"measures": [["2016-01-12T00:00:00+00:00", 86400.0, 1.0], ["2016-01-13T00:00:00+00:00", 86400.0, 1.0], ["2016-01-19T00:00:00+00:00", 86400.0, 1.0], ["2016-01-21T00:00:00+00:00", 86400.0, 1.0], ["2016-01-22T00:00:00+00:00", 86400.0, 1.0], ["2016-01-28T00:00:00+00:00", 86400.0, 1.0], ["2016-01-29T00:00:00+00:00", 86400.0, 1.0]], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "572cdbb9-a21e-40d6-a1ce-abca972609df"}}, {"measures": [["2016-01-12T00:00:00+00:00", 86400.0, 1.0], ["2016-01-13T00:00:00+00:00", 86400.0, 1.0], ["2016-01-19T00:00:00+00:00", 86400.0, 1.0], ["2016-01-21T00:00:00+00:00", 86400.0, 1.0], ["2016-01-22T00:00:00+00:00", 86400.0, 1.0], ["2016-01-28T00:00:00+00:00", 86400.0, 1.0], ["2016-01-29T00:00:00+00:00", 86400.0, 1.0]], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "34126752-34f2-43ce-8722-86963075fdc9"}}, {"measures": [["2016-01-12T00:00:00+00:00", 86400.0, 1.0], ["2016-01-13T00:00:00+00:00", 86400.0, 1.0], ["2016-01-19T00:00:00+00:00", 86400.0, 1.0], ["2016-01-21T00:00:00+00:00", 86400.0, 1.0], ["2016-01-22T00:00:00+00:00", 86400.0, 1.0], ["2016-01-28T00:00:00+00:00", 86400.0, 1.0], ["2016-01-29T00:00:00+00:00", 86400.0, 1.0]], "group": {"project_id": "0ae5f95d-febd-4d17-baa1-e72a0740a5df", "flavor_id": "843716b8-1c7a-4522-83f2-836b80a3f11d"}}, {"measures": [["2016-01-12T00:00:00+00:00", 86400.0, 1.0], ["2016-01-13T00:00:00+00:00", 86400.0, 1.0], ["2016-01-19T00:00:00+00:00", 86400.0, 1.0], ["2016-01-21T00:00:00+00:00", 86400.0, 1.0], ["2016-01-22T00:00:00+00:00", 86400.0, 1.0], ["2016-01-28T00:00:00+00:00", 86400.0, 81.0], ["2016-01-29T00:00:00+00:00", 86400.0, 13.0]], "group": {"project_id": "62e08edf-df81-4898-8ae7-0568fe8be307", "flavor_id": "572cdbb9-a21e-40d6-a1ce-abca972609df"}}]