How to find all combinations (subset) of any size of an array in postgresql -



How to find all combinations (subset) of any size of an array in postgresql -

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array combinations without repetition 1 reply

given array, how find combinations (subsets) of elements of size in postgresql. example, given array [1, 2, 3, 4] combinations of size 3 be

[1, 2, 3], [1, 2, 4], [1, 3, 4], [2, 3, 4]

order not of import in combinations , hence [1, 2, 3] , [3, 2, 1] considered same combination.

update: size of combinations required must specified @ run-time parameter, same function/query can used find combinations of size n <= size of array. the existing solution works combinations of size 3 , needs 1 additional cross bring together every increment in size, not practical.

the next function produces combinations of requested size set of rows 1 combination per row:

create or replace function get_combinations(source anyarray, size int) returns setof anyarray $$ recursive combinations(combination, indices) ( select source[i:i], array[i] generate_subscripts(source, 1) union select c.combination || source[j], c.indices || j combinations c, generate_subscripts(source, 1) j j > all(c.indices) , array_length(c.combination, 1) < size ) select combination combinations array_length(combination, 1) = size; $$ language sql;

this function polymorphic in array type.

arrays postgresql combinations plpgsql

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