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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
```cli
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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