Postgres/Postgis - Querying all values in clipped raster - sql

Question

I'm currently using Postgres 9.1
My goal is to clip a PostGIS raster with a polygon. Then I would like either an postgres array or delimited set of values for each of the raster pixels that are contained within that polygon. Here is the query I have gotten so far:
SELECT p.gid, (ST_ValueCount(ST_Clip(r.rast, p.geom))).value AS fval
FROM temp_raster AS r, temp_shapefile AS p
WHERE (r.start_time = 1384516800)
GROUP BY gid, fval;
This will output:
gid | fcstval
-----+---------
1 | 0
1 | 2
2 | 0
2 | 2
3 | 5
4 | 0
4 | 1
4 | 2
4 | 3
4 | 5
This data is good, but I would like a set of values for each gid like this:
gid | fcstval
-----+----------
1 | 0,2
2 | 0,2
3 | 5
4 | 0,1,2,3,5
The trouble I'm having is trying to then get these values aggregated into either an array or delimited string. Here's my attempt at an array:
SELECT p.gid, array_agg((ST_ValueCount(ST_Clip(r.rast, p.geom))).value) AS fval
FROM temp_raster AS r, temp_shapefile AS p
WHERE (r.start_time = 1384516800)
GROUP BY gid;
This doesn't work, and provides the error:
ERROR: set-valued function called in context that cannot accept a set
My guess is this is because I can't call array_agg in this way. I'm having a bit of difficulty figuring out how to do this otherwise. A subquery perhaps? I haven't been able to come up with anything yet though to get this working.
Thanks for any help!

Answer 1

Okay I think I figured it out for arrays. If I want it in a string, I can just convert my array to a string. However if anyone has any suggestions of cleaning this up I would appreciate it, as this doesn't seem like the simplest markup
SELECT p.gid, array_agg((subquery).tempval) as fcstval
FROM pih_raster AS r, hwy_pih_vertex_buf AS p,
(
SELECT p.gid AS tempgid, (ST_ValueCount(ST_Clip(r.rast, p.geom))).value AS tempval
FROM pih_raster AS r, hwy_pih_vertex_buf AS p
WHERE (r.start_time <= 1384624800) GROUP BY tempgid, tempval
) AS subquery
WHERE (r.start_time <= 1384624800) AND ((subquery).tempgid = gid) GROUP BY p.gid;
Here's the output:
gid | fcstval
-----+-------------
1 | {0,2}
2 | {0,2}
3 | {5}
4 | {0,1,2,3,5}