Summing arrays in conjunction with GROUP BY - postgresql

Question

I've got some periodic counter data (like once a second) from different objects that I wish to combine into an hourly total.
If I do it with separate column names, it's pretty straightforward:
CREATE TABLE ts1 (
id INTEGER,
ts TIMESTAMP,
count0 integer,
count1 integer,
count2 integer
);
INSERT INTO ts1 VALUES
(1, '2017-12-07 10:37:48', 10, 20, 50),
(2, '2017-12-07 10:37:48', 13, 7, 88),
(1, '2017-12-07 10:37:49', 12, 23, 34),
(2, '2017-12-07 10:37:49', 11, 13, 46),
(1, '2017-12-07 10:37:50', 8, 33, 80),
(2, '2017-12-07 10:37:50', 9, 3, 47),
(1, '2017-12-07 10:37:51', 17, 99, 7),
(2, '2017-12-07 10:37:51', 9, 23, 96);
SELECT id, date_trunc('hour', ts + '1 hour') nts,
sum(count0), sum(count1), sum(count2)
FROM ts1 GROUP BY id, nts;
id | nts | sum | sum | sum
----+---------------------+-----+-----+-----
1 | 2017-12-07 11:00:00 | 47 | 175 | 171
2 | 2017-12-07 11:00:00 | 42 | 46 | 277
(2 rows)
The problem is that different objects have different numbers of counts (though each particular object's rows -- ones sharing the same ID -- all have the same number of counts). Hence I want to use an array.
The corresponding table looks like this:
CREATE TABLE ts2 (
id INTEGER,
ts TIMESTAMP,
counts INTEGER[]
);
INSERT INTO ts2 VALUES
(1, '2017-12-07 10:37:48', ARRAY[10, 20, 50]),
(2, '2017-12-07 10:37:48', ARRAY[13, 7, 88]),
(1, '2017-12-07 10:37:49', ARRAY[12, 23, 34]),
(2, '2017-12-07 10:37:49', ARRAY[11, 13, 46]),
(1, '2017-12-07 10:37:50', ARRAY[8, 33, 80]),
(2, '2017-12-07 10:37:50', ARRAY[9, 3, 47]),
(1, '2017-12-07 10:37:51', ARRAY[17, 99, 7]),
(2, '2017-12-07 10:37:51', ARRAY[9, 23, 96]);
I have looked at this answer https://stackoverflow.com/a/24997565/1076479 and I get the general gist of it, but I cannot figure out how to get the correct rows summed together when I try to combine it with the grouping by id and timestamp.
For example, with this I get all the rows, not just the ones with matching id and timestamp:
SELECT id, date_trunc('hour', ts + '1 hour') nts, ARRAY(
SELECT sum(elem) FROM ts2 t, unnest(t.counts)
WITH ORDINALITY x(elem, rn) GROUP BY rn ORDER BY rn
) FROM ts2 GROUP BY id, nts;
id | nts | array
----+---------------------+--------------
1 | 2017-12-07 11:00:00 | {89,221,448}
2 | 2017-12-07 11:00:00 | {89,221,448}
(2 rows)
FWIW, I'm using postgresql 9.6

Answer 1

The problem with you original query is that you're summing all elements, because GROUP BY id, nts is executed in outer query. Combining a CTE with LATERAL JOIN would do the trick:
WITH tmp AS (
SELECT
id,
date_trunc('hour', ts + '1 hour') nts,
sum(elem) AS counts
FROM
ts2
LEFT JOIN LATERAL unnest(counts) WITH ORDINALITY x(elem, rn) ON TRUE
GROUP BY
id, nts, rn
)
SELECT id, nts, array_agg(counts) FROM tmp GROUP BY id, nts