ZRANDMEMBER

Syntax
ZRANDMEMBER key [count [WITHSCORES]]
Available since:
6.2.0
Time complexity:
O(N) where N is the number of members returned
ACL categories:
@read, @sortedset, @slow,

When called with just the key argument, return a random element from the sorted set value stored at key.

If the provided count argument is positive, return an array of distinct elements. The array's length is either count or the sorted set's cardinality (ZCARD), whichever is lower.

If called with a negative count, the behavior changes and the command is allowed to return the same element multiple times. In this case, the number of returned elements is the absolute value of the specified count.

The optional WITHSCORES modifier changes the reply so it includes the respective scores of the randomly selected elements from the sorted set.

Return

Bulk string reply: without the additional count argument, the command returns a Bulk Reply with the randomly selected element, or nil when key does not exist.

Array reply: when the additional count argument is passed, the command returns an array of elements, or an empty array when key does not exist. If the WITHSCORES modifier is used, the reply is a list elements and their scores from the sorted set.

Examples

ZADD dadi 1 uno 2 due 3 tre 4 quattro 5 cinque 6 sei ZRANDMEMBER dadi ZRANDMEMBER dadi ZRANDMEMBER dadi -5 WITHSCORES

Specification of the behavior when count is passed

When the count argument is a positive value this command behaves as follows:

  • No repeated elements are returned.
  • If count is bigger than the cardinality of the sorted set, the command will only return the whole sorted set without additional elements.
  • The order of elements in the reply is not truly random, so it is up to the client to shuffle them if needed.

When the count is a negative value, the behavior changes as follows:

  • Repeating elements are possible.
  • Exactly count elements, or an empty array if the sorted set is empty (non-existing key), are always returned.
  • The order of elements in the reply is truly random.
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