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ZINTER

Computes the intersection of multiple sorted sets and returns the resulting members. By default, the resulting members are sorted by their score in ascending order.

Syntax​

ZINTER numkeys key [key ...] [WEIGHTS weight [weight ...]] [AGGREGATE SUM|MIN|MAX] [WITHSCORES]

Parameters​

  • numkeys: The number of sorted sets involved in the intersection.
  • key: The name of each sorted set involved in the operation.
  • 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 elements that exist across multiple sets. The options are SUM (default), MIN, or MAX.
  • WITHSCORES: Optional. Returns the resulting members with their scores.

Details​

  • Available since: 6.2.0
  • Time complexity: O(N*K + M log(M)) where N is the size of the input sorted sets, K is the number of sets, and M is the number of elements in the result.
  • ACL categories: @read, @sortedset, @slow

The ZINTER command computes the intersection of the specified sorted sets. The resulting set consists of members that are present in every one of the specified sets. If a member is present in multiple sets, its score in the result is calculated based on the WEIGHTS and AGGREGATE options.

Examples​

Basic Usage​

Assume we have three sorted sets:

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

To find the intersection of these sets:

ZINTER 3 set1 set2 set3

This will return:

1) "c"

Using the WEIGHTS Option​

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

ZINTER 3 set1 set2 set3 WEIGHTS 2 3 1

This will compute the intersection with weighted scores.

Using the AGGREGATE Option​

To find the intersection but keep the minimum score from the sets for each member:

ZINTER 3 set1 set2 set3 AGGREGATE MIN

Including Scores in the Result​

To return the members of the intersection along with their scores:

ZINTER 3 set1 set2 set3 WITHSCORES

This will return:

1) "c"
2) "score_of_c"

Edge Cases​

  • If the intersection is empty, ZINTER will return an empty array.
  • If the key does not exist, it is treated as an empty set.
  • If any of the keys refer to non-sorted set data types, an error is returned.

RESP2/RESP3 Reply​

  • Array reply: list of members in the intersection, optionally with their scores if WITHSCORES is specified.