Event grouping in time series - sql

Question

I'm trying to build groups of precipitation events in my measurement data. I got a time, a measurement value and a flag noting if it's was raining:
00:00, 32.4, 0
00:10, 32.4, 0
00:20, 32.6, 1
00:30, 32.7, 1
00:40, 32.9, 1
00:50, 33.2, 1
01:00, 33.2, 0
01:10, 33.2, 0
01:20, 33.2, 0
01:30, 33.5, 1
01:40, 33.6, 1
01:50, 33.6, 0
02:00, 33.6, 0
...
Now I'd like to generate an event id for the precipitation events:
00:00, 32.4, 0, NULL
00:10, 32.4, 0, NULL
00:20, 32.6, 1, 1
00:30, 32.7, 1, 1
00:40, 32.9, 1, 1
00:50, 33.2, 1, 1
01:00, 33.2, 0, NULL
01:10, 33.2, 0, NULL
01:20, 33.2, 0, NULL
01:30, 33.5, 1, 2
01:40, 33.6, 1, 2
01:50, 33.6, 0, NULL
02:00, 33.6, 0, NULL
...
Then I'll be able to use grouping to summarize the events. Any hint how to do this in Oracle is much appreciated.
So far I was able to calculate the mentioned flag and the diff to the last row:
SELECT
measured_at,
station_id
ps, -- precipitation sum
ps - lag(ps, 1, NULL) OVER (ORDER BY measured_at ASC) as p, -- precipitation delta
CASE
WHEN ps - lag(ps, 1, NULL) OVER (ORDER BY measured_at ASC) > 0 THEN 1
ELSE 0
END as rainflag
FROM measurements;
I think it must be possible to generate the required event id somehow, but can't figure it out. Thanks for your time!
Final solution using mt0 answer:
DROP TABLE events;
CREATE TABLE events (measured_at, station_id, ps) AS
SELECT TO_DATE('2016-05-01 12:00', 'YYYY-MM-DD HH24:MI'), 'XYZ', 32.4 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 12:10', 'YYYY-MM-DD HH24:MI'), 'XYZ', 32.6 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 12:20', 'YYYY-MM-DD HH24:MI'), 'XYZ', 32.7 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 12:30', 'YYYY-MM-DD HH24:MI'), 'XYZ', 32.9 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 12:40', 'YYYY-MM-DD HH24:MI'), 'XYZ', 33.2 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 12:50', 'YYYY-MM-DD HH24:MI'), 'XYZ', 33.2 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 13:00', 'YYYY-MM-DD HH24:MI'), 'XYZ', 33.2 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 13:10', 'YYYY-MM-DD HH24:MI'), 'XYZ', 33.2 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 13:20', 'YYYY-MM-DD HH24:MI'), 'XYZ', 33.5 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 13:30', 'YYYY-MM-DD HH24:MI'), 'XYZ', 33.6 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 13:40', 'YYYY-MM-DD HH24:MI'), 'XYZ', 33.6 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 13:50', 'YYYY-MM-DD HH24:MI'), 'XYZ', 33.5 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 17:00', 'YYYY-MM-DD HH24:MI'), 'XYZ', 39.1 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 17:10', 'YYYY-MM-DD HH24:MI'), 'XYZ', 39.2 FROM DUAL UNION ALL
SELECT TO_DATE('2016-05-01 17:20', 'YYYY-MM-DD HH24:MI'), 'XYZ', 39.2 FROM DUAL;
WITH
flagged AS (
SELECT
measured_at,
station_id,
ps,
CASE
WHEN measured_at - lag(measured_at, 1, NULL) OVER (ORDER BY measured_at) = (1/144) THEN ps - lag(ps, 1, NULL) OVER (ORDER BY measured_at)
ELSE NULL
END as delta_p,
CASE
WHEN ps - lag(ps, 1, NULL) OVER (ORDER BY measured_at) > 0 THEN 1
ELSE 0
END AS rain
FROM events
),
eventmarked AS (
SELECT
f.*,
CASE
WHEN f.delta_p >= 0 THEN f.delta_p
ELSE NULL
END AS p,
CASE rain
WHEN 1 THEN COUNT(1) OVER (ORDER BY measured_at) - SUM(rain) OVER (ORDER BY measured_at)
END as event
FROM flagged f
),
summarized AS (
SELECT
em.*,
sum(CASE p WHEN 0 THEN NULL ELSE p END) OVER (PARTITION BY event ORDER BY measured_at) as e_ps
FROM eventmarked em
)
SELECT measured_at, station_id, ps, p, e_ps FROM summarized
ORDER BY measured_at;

Answer 1

Oracle Setup:
CREATE TABLE events ( measured_at, station_id, ps ) AS
SELECT '00:00', 32.4, 0 FROM DUAL UNION ALL
SELECT '00:10', 32.4, 0 FROM DUAL UNION ALL
SELECT '00:20', 32.6, 1 FROM DUAL UNION ALL
SELECT '00:30', 32.7, 1 FROM DUAL UNION ALL
SELECT '00:40', 32.9, 1 FROM DUAL UNION ALL
SELECT '00:50', 33.2, 1 FROM DUAL UNION ALL
SELECT '01:00', 33.2, 0 FROM DUAL UNION ALL
SELECT '01:10', 33.2, 0 FROM DUAL UNION ALL
SELECT '01:20', 33.2, 0 FROM DUAL UNION ALL
SELECT '01:30', 33.5, 1 FROM DUAL UNION ALL
SELECT '01:40', 33.6, 1 FROM DUAL UNION ALL
SELECT '01:50', 33.6, 0 FROM DUAL UNION ALL
SELECT '02:00', 33.6, 0 FROM DUAL;
Query:
SELECT measured_at,
station_id,
ps,
CASE WHEN rainflag IS NOT NULL THEN DENSE_RANK() OVER ( ORDER BY rainflag ) END AS rainflag
FROM (
SELECT e.*,
CASE ps
WHEN 1
THEN COUNT( 1 ) OVER ( ORDER BY measured_at )
- SUM( ps ) OVER ( ORDER BY measured_at )
END AS rainflag
FROM events e
)
ORDER BY measured_at;
Query 2
SELECT measured_at,
station_id,
ps,
CASE ps WHEN 1
THEN SUM( rainflag ) OVER ( ORDER BY measured_at )
END AS rainflag
FROM (
SELECT e.*,
CASE WHEN ps > LAG( ps, 1, 0 ) OVER ( ORDER BY measured_at )
THEN 1
END AS rainflag
FROM events e
);
Output:
MEASURED_AT STATION_ID PS RAINFLAG
----------- ---------- ---------- ----------
00:00 32.4 0
00:10 32.4 0
00:20 32.6 1 1
00:30 32.7 1 1
00:40 32.9 1 1
00:50 33.2 1 1
01:00 33.2 0
01:10 33.2 0
01:20 33.2 0
01:30 33.5 1 2
01:40 33.6 1 2
01:50 33.6 0
02:00 33.6 0

Answer 2

Alternative solution using only LAG function.
In the subquery the column PS2 marks the rain started events. The main query simple sums this flag while ignoring the time that is not raining.
with ev as (
select measured_at, station_id, ps,
case when ps = 1 and lag(ps,1,0) over (order by measured_at) = 0
then 1 else 0 end ps2
from events)
select measured_at, station_id, ps, ps2,
case when ps = 1 then
sum(ps2) over (order by measured_at) end rf
from ev
;
MEASURED_AT STATION_ID PS PS2 RF
----------- ---------- ---------- ---------- ----------
00:00 32,4 0 0
00:10 32,4 0 0
00:20 32,6 1 1 1
00:30 32,7 1 0 1
00:40 32,9 1 0 1
00:50 33,2 1 0 1
01:00 33,2 0 0
01:10 33,2 0 0
01:20 33,2 0 0
01:30 33,5 1 1 2
01:40 33,6 1 0 2
01:50 33,6 0 0
02:00 33,6 0 0