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ZUNIONSTORE

Computes the union of multiple sorted sets, aggregates their scores, and stores the result in a new sorted set.

Syntax​

ZUNIONSTORE destination numkeys key [key ...] [WEIGHTS weight [weight ...]] [AGGREGATE SUM|MIN|MAX]

Parameters​

  • destination: The key where the result of the union will be stored.
  • numkeys: The number of sorted sets involved in the operation.
  • key: The name of each sorted set involved in the union.
  • WEIGHTS: Optional. Specifies a multiplication factor for each sorted set’s scores. If not specified, the default weight is 1 for all sets.
  • AGGREGATE: Optional. Specifies how to combine the scores of members that exist across multiple sets. The options are SUM (default), MIN, or MAX.

Details​

  • Available since: 2.0.0
  • Time complexity: O(N) + O(M log(M)) with N being the sum of the input sorted sets, and M being the number of elements in the resulting set.
  • ACL categories: @write, @sortedset, @slow

The ZUNIONSTORE command computes the union of the specified sorted sets, aggregates their scores, and stores the resulting sorted set at the destination key. The resulting members are ordered by their scores in ascending order.

Aggregate Options​

  • SUM: The scores of members that exist in multiple sets are summed.
  • MIN: The resulting score of a member is the minimum of its scores across the input sets.
  • MAX: The resulting score of a member is the maximum of its scores across the input sets.

Weights​

The WEIGHTS option allows you to multiply the scores of the members in each input sorted set by a specific factor before applying the aggregation.

Examples​

Basic Usage​

Assume we have three sorted sets:

ZADD set1 1 "a" 2 "b"
ZADD set2 2 "a" 3 "c"
ZADD set3 3 "a" 4 "d"

To compute the union of these sets and store the result in resultset:

ZUNIONSTORE resultset 3 set1 set2 set3

After running this command, the resultset will contain:

ZRANGE resultset 0 -1 WITHSCORES

This will return:

1) "b"
2) "2"
3) "c"
4) "3"
5) "d"
6) "4"
7) "a"
8) "6"

Using WEIGHTS​

To multiply the scores of set1 by 2, set2 by 3, and set3 by 1 before computing the union and storing the result:

ZUNIONSTORE resultset 3 set1 set2 set3 WEIGHTS 2 3 1

This will store the result with weighted scores in resultset.

Using AGGREGATE​

To compute the union and store the result in resultset while keeping the maximum score for each member:

ZUNIONSTORE resultset 3 set1 set2 set3 AGGREGATE MAX

Edge Cases​

  • If the destination key already exists, it will be overwritten with the new result.
  • If a key does not exist, it is treated as an empty set.
  • If any of the input sets are empty, the result will be an empty set.
  • If any of the keys refer to non-sorted set data types, an error is returned.

RESP2/RESP3 Reply​

  • Integer reply: the number of elements in the resulting sorted set stored at the destination key.