Normalized histogram in psql

agg_histogram.sql

-- from: https://wiki.postgresql.org/wiki/Aggregate_Histogram

CREATE OR REPLACE FUNCTION hist_sfunc (state INTEGER[], val REAL, min REAL, max REAL, nbuckets INTEGER) RETURNS INTEGER[] AS $$
DECLARE
  bucket INTEGER;
  i INTEGER;
BEGIN
  -- width_bucket uses nbuckets + 1 (!) and starts at 1.
  bucket := width_bucket(val, min, max, nbuckets - 1) - 1;
 
  -- Init the array with the correct number of 0's so the caller doesn't see NULLs
  IF state[0] IS NULL THEN
    FOR i IN SELECT * FROM generate_series(0, nbuckets - 1) LOOP
      state[i] := 0;
    END LOOP;
  END IF;
 
  state[bucket] = state[bucket] + 1;
 
  RETURN state;
END;
$$ LANGUAGE plpgsql IMMUTABLE;
 
-- Tell Postgres how to use the new function
DROP AGGREGATE IF EXISTS histogram (REAL, REAL, REAL, INTEGER);
CREATE AGGREGATE histogram (REAL, REAL, REAL, INTEGER) (
       SFUNC = hist_sfunc,
       STYPE = INTEGER[]
);

array_each.sql

-- from: http://stackoverflow.com/a/8584506/21115

SELECT array_agg(ROUND(n, 2)) FROM unnest(ARRAY[1.53224,0.23411234]) AS n

sum_anyarray.sql

-- from: http://www.postgresql.org/message-id/[email protected]

create or replace function sum_decimal_array( anyarray )
returns bigint
as $$
   select sum($1[i])
   from generate_series(
          array_lower($1,1),
          array_upper($1,1)
        ) g(i);
$$ language sql immutable;
CREATE FUNCTION

My goal is to get a normalized output from histogram, such that sum_decimal_array of the output would be 1.

I believe I have all the component here, but I can't get them to come together.

Trying to get my head around how this would work, I tried:

array_agg(unnest(histogram(...)))

But then I get:

ERROR:  aggregate function calls cannot be nested

Which makes me think I'm missing something here.