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Jenks: Iterate increasing the number of moved elements exponentially

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This commit is contained in:
Raul Marin 2018-09-11 19:22:48 +02:00
parent 7e131ac88d
commit d2a00852a8
1 changed files with 48 additions and 16 deletions
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64
scripts-available/CDB_JenksBins.sql
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@ -130,7 +130,6 @@ BEGIN
IF curr_result[1] > best_result[1] THEN
best_result = curr_result;
j = j-1; -- if we found a better result, add one more search
END IF;
j = j+1;
@ -163,11 +162,15 @@ DECLARE
class_avg numeric;
class_dev numeric;
class_max_i INT;
class_min_i INT;
class_max_i INT = 0;
class_min_i INT = 0;
dev_max numeric;
dev_min numeric;
best_classes INT[] = classes;
best_gvf numeric[];
best_avg numeric[];
move_elements INT = 1;
reply numeric[];
@ -201,7 +204,9 @@ BEGIN
END IF;
END LOOP;
-- We copy the values to avoid recalculation when a failure happens
best_avg = arr_avg;
best_gvf = arr_gvf;
iterations = 0;
LOOP
@ -211,10 +216,30 @@ BEGIN
-- calculate our new GVF
SELECT sdam - sum(e) INTO new_gvf FROM ( SELECT unnest(arr_gvf) as e ) x;
-- if no improvement was made, exit
IF new_gvf <= gvf OR class_max_i = class_min_i THEN EXIT; END IF;
-- Check if any improvement was made
IF new_gvf <= gvf THEN
-- If we were moving too many elements, go back and move less
IF move_elements <= 2 OR class_max_i = class_min_i THEN
EXIT;
END IF;
-- We search for classes with the min and max deviation
move_elements = GREATEST(move_elements / 8, 1);
-- Rollback from saved statuses
classes = best_classes;
new_gvf = gvf;
i = class_min_i;
LOOP
arr_avg[i] = best_avg[i];
arr_gvf[i] = best_gvf[i];
IF i = class_max_i THEN EXIT; END IF;
i = i + 1;
END LOOP;
END IF;
-- We search for the classes with the min and max deviation
i = 1;
class_min_i = 1;
class_max_i = 1;
@ -240,60 +265,68 @@ BEGIN
gvf = new_gvf;
best_classes = classes;
-- Iterate by moving an element from class_max_i to class_min_i
-- Limit the moved elements as to not remove everything from class_max_i
move_elements = LEAST(move_elements, classes[class_max_i][2] - classes[class_max_i][1]);
-- Move `move_elements` from class_max_i to class_min_i
IF class_min_i < class_max_i THEN
i := class_min_i;
LOOP
IF i = class_max_i THEN EXIT; END IF;
classes[i][2] = classes[i][2] + 1;
classes[i][2] = classes[i][2] + move_elements;
i := i + 1;
END LOOP;
i := class_max_i;
LOOP
IF i = class_min_i THEN EXIT; END IF;
classes[i][1] = classes[i][1] + 1;
classes[i][1] = classes[i][1] + move_elements;
i := i - 1;
END LOOP;
ELSE
i := class_min_i;
LOOP
IF i = class_max_i THEN EXIT; END IF;
classes[i][1] = classes[i][1] - 1;
classes[i][1] = classes[i][1] - move_elements;
i := i - 1;
END LOOP;
i := class_max_i;
LOOP
IF i = class_min_i THEN EXIT; END IF;
classes[i][2] = classes[i][2] - 1;
classes[i][2] = classes[i][2] - move_elements;
i := i + 1;
END LOOP;
END IF;
-- Recalculate avg and deviation for the affected classes
-- Recalculate avg and deviation ONLY for the affected classes
i = LEAST(class_min_i, class_max_i);
class_max_i = GREATEST(class_min_i, class_max_i);
class_min_i = i;
LOOP
-- Get class mean
SELECT (sum(v * w) / sum(w)) INTO class_avg FROM (
SELECT unnest(in_matrix[1:1][classes[i][1]:classes[i][2]]) as v,
unnest(in_matrix[2:2][classes[i][1]:classes[i][2]]) as w
) x;
-- Get class deviation
SELECT sum((class_avg - v)^2 * w) INTO class_dev FROM (
SELECT unnest(in_matrix[1:1][classes[i][1]:classes[i][2]]) as v,
unnest(in_matrix[2:2][classes[i][1]:classes[i][2]]) as w
) x;
-- Save status (in case it's needed for rollback) and store the new one
best_avg[i] = arr_avg[i];
arr_avg[i] = class_avg;
best_gvf[i] = arr_gvf[i];
arr_gvf[i] = class_dev;
IF i = class_max_i THEN EXIT; END IF;
i = i + 1;
END LOOP;
move_elements = move_elements * 2;
END LOOP;
i = 1;
@ -311,4 +344,3 @@ BEGIN
END;
$$ LANGUAGE PLPGSQL IMMUTABLE PARALLEL SAFE;