Re: Subtract one array from another, both with non-unique elements

Hello again,

I could not find a solution neither
at http://postgres.cz/wiki/Array_based_functions
nor at https://github.com/JDBurnZ/postgresql-anyarray

So I have written my own stored function
to subtract one non-unique array from another
(like swapping tiles in a word game):

DROP FUNCTION IF EXISTS words_array_subtract(anyarray, anyarray);
CREATE OR REPLACE FUNCTION words_array_subtract(from_array anyarray,
remove_array anyarray)
RETURNS anyarray AS
$func$
DECLARE
i integer;
j integer;
from_ignore boolean[];
remove_ignore boolean[];
result_array from_array%TYPE := '{}';
BEGIN
IF NOT from_array @> remove_array THEN
RAISE EXCEPTION '% does not contain %', from_array,
remove_array;
END IF;

from_ignore := ARRAY_FILL(FALSE,
ARRAY[ARRAY_LENGTH(from_array, 1)]);
remove_ignore := ARRAY_FILL(FALSE,
ARRAY[ARRAY_LENGTH(remove_array, 1)]);

RAISE NOTICE 'from_ignore = %', from_ignore;
RAISE NOTICE 'remove_ignore = %', remove_ignore;

FOR i IN ARRAY_LOWER(from_array,
1)..ARRAY_UPPER(from_array, 1) LOOP
FOR j IN ARRAY_LOWER(remove_array,
1)..ARRAY_UPPER(remove_array, 1) LOOP
IF from_ignore[i] = FALSE AND
remove_ignore[j] = FALSE AND
from_array[i] = remove_array[j] THEN
from_ignore[i] := TRUE;
remove_ignore[j] := TRUE;
END IF;
END LOOP;
END LOOP;

FOR i IN ARRAY_LOWER(from_array,
1)..ARRAY_UPPER(from_array, 1) LOOP
IF from_ignore[i] = FALSE THEN
result_array := ARRAY_APPEND(result_array,
from_array[i]);
END IF;
END LOOP;

RETURN result_array;
END;
$func$ LANGUAGE plpgsql;

# select words_array_subtract(ARRAY['A','A','B','B','C'], ARRAY['A','B']);
NOTICE: from_ignore = {f,f,f,f,f}
NOTICE: remove_ignore = {f,f}
words_array_subtract
----------------------
{A,B,C}
(1 row)

# select words_array_subtract(ARRAY[1,2,2,3,4,4, 5], ARRAY[2,4,4]);
NOTICE: from_ignore = {f,f,f,f,f,f,f}
NOTICE: remove_ignore = {f,f,f}
words_array_subtract
----------------------
{1,2,3,5}
(1 row)

If you have any improvement proposals please tell me.

Regards
Alex