How to apply a function to each element of an array column in Postgres?

First, turn the array into a set using unnest:

> SELECT n FROM unnest(ARRAY[1.53224,0.23411234]) AS n;     n      ------------    1.53224 0.23411234(2 rows)

Then, apply an expression to the column:

> SELECT ROUND(n, 2) FROM unnest(ARRAY[1.53224,0.23411234]) AS n; round -------  1.53  0.23(2 rows)

Finally, use array_agg to turn the set back into an array:

> SELECT array_agg(ROUND(n, 2)) FROM unnest(ARRAY[1.53224,0.23411234]) AS n;  array_agg  ------------- {1.53,0.23}(1 row)

postgres=# select array(select round(unnest(array[1.2,2.4,3,4])));   array   -----------{1,2,3,4}(1 row)

You may need to create a stored function. Here is the one that does what you need:

CREATE OR REPLACE FUNCTION array_round(float[], int)RETURNS float[]AS$$DECLARE   arrFloats ALIAS FOR $1;   roundParam ALIAS FOR $2;   retVal float[];BEGIN   FOR I IN array_lower(arrFloats, 1)..array_upper(arrFloats, 1) LOOP    retVal[I] := round(CAST(arrFloats[I] as numeric), roundParam);   END LOOP;RETURN retVal;END;$$LANGUAGE plpgsql    STABLE RETURNS NULL ON NULL INPUT;

Then call something like this:

# SELECT array_round(ARRAY[1.53224,0.23411234], 2); array_round ------------- {1.53,0.23}(1 row)