ARRAY_SHUFFLE
Description
Randomly shuffles the order of elements in an array, preserving the elements and their count. Returns NULL if the input array or seed is NULL. SHUFFLE is an alias for this function.
In the Doris 4.1 series since 4.1.5, seed must be a constant. It accepts any BIGINT value, including negative values, and uses all 64 bits. Constant arrays are also shuffled separately for each row, so the same seed may produce a different result from earlier versions. Earlier 4.1 versions used only the seed of the first row in each batch, rejected negative seeds and seeds greater than 4294967295, and produced the same order on every row for constant arrays.
Syntax
ARRAY_SHUFFLE(<arr> [, <seed>])
Parameters
| Parameter | Description |
|---|---|
<arr> | ARRAY to shuffle. |
<seed> | Optional constant BIGINT random seed. Constant expressions are supported. If omitted, each batch uses a new random seed. |
Return Value
Returns an array of the same type as the input, with elements randomly reordered. Element count and types are preserved. Returns NULL if the array or seed is NULL, and returns an empty array for an empty input array.
Rows are processed in batches. With a specified seed, each batch starts a random sequence from that seed, and its rows use that sequence in order. A row's permutation can therefore depend on batch boundaries. Specifying a seed does not guarantee identical permutations for identical arrays. Constant arrays are also shuffled separately for each row.
Example
Sorting the shuffled array verifies that its elements are preserved. Both negative seeds and constant expressions are valid:
SELECT ARRAY_SORT(ARRAY_SHUFFLE([1, 2, 3, 4], -1)),
ARRAY_SORT(ARRAY_SHUFFLE([1, 2, 3, 4], 1 + 1));
[1, 2, 3, 4] [1, 2, 3, 4]
NULL and empty arrays:
SELECT ARRAY_SHUFFLE(CAST(NULL AS ARRAY<INT>), 1),
ARRAY_SHUFFLE([1, 2, 3], NULL), ARRAY_SHUFFLE([], 1);
NULL NULL []
Using a column as the seed reports an error containing:
SELECT ARRAY_SHUFFLE([1, 2, 3], number) FROM numbers("number" = "2");
The seed of array_shuffle must be a constant