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ZDIFFSTORE

Computes the difference between the first sorted set and all successive sorted sets, and stores the resulting sorted set in a new key.

Syntax​

ZDIFFSTORE destination numkeys key [key ...]

Parameters​

  • destination: The key where the result of the difference will be stored.
  • numkeys: The number of sorted sets involved in the operation, including the first set.
  • key: The name of each sorted set involved in the operation.

Details​

  • Available since: 6.2.0
  • Time complexity: O(N + M log(M)) where N is the size of the input sorted sets and M is the size of the result set.
  • ACL categories: @write, @sortedset, @slow

The ZDIFFSTORE command computes the difference between the first sorted set and all the successive sorted sets, similar to ZDIFF, but instead of returning the result, it stores the resulting sorted set at the specified destination key.

Examples​

Assume we have three sorted sets:

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

To compute the difference between set1 and the other sets, and store the result in diffset:

ZDIFFSTORE diffset 3 set1 set2 set3

After running this command, the diffset will contain:

ZRANGE diffset 0 -1 WITHSCORES

This will return:

1) "b"
2) "2"

Edge Cases​

  • If the destination key already exists, it will be overwritten with the new result.
  • If the first set is empty, ZDIFFSTORE will store an empty sorted set at the destination key.
  • If there are no members left after subtracting all the successive sets, an empty sorted set will be stored at the destination key.
  • If the destination key refers to a non-sorted set data type, it will be replaced by the result sorted set.

RESP2/RESP3 Reply​

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