SPOP

Syntax

  1. SPOP key [count]

Time complexity: Without the count argument O(1), otherwise O(N) where N is the value of the passed count.

Removes and returns one or more random members from the set value store at key.

This operation is similar to SRANDMEMBER, that returns one or more random elements from a set but does not remove it.

By default, the command pops a single member from the set. When provided with the optional count argument, the reply will consist of up to count members, depending on the set’s cardinality.

Return

When called without the count argument:

Bulk string reply: the removed member, or nil when key does not exist.

When called with the count argument:

Array reply: the removed members, or an empty array when key does not exist.

Examples

  1. dragonfly> SADD myset "one"
  2. (integer) 1
  3. dragonfly> SADD myset "two"
  4. (integer) 1
  5. dragonfly> SADD myset "three"
  6. (integer) 1
  7. dragonfly> SPOP myset
  8. "one"
  9. dragonfly> SMEMBERS myset
  10. 1) "three"
  11. 2) "two"
  12. dragonfly> SADD myset "four"
  13. (integer) 1
  14. dragonfly> SADD myset "five"
  15. (integer) 1
  16. dragonfly> SPOP myset 3
  17. 1) "three"
  18. 2) "two"
  19. 3) "four"
  20. dragonfly> SMEMBERS myset
  21. 1) "five"

Distribution of returned elements

Note that this command is not suitable when you need a guaranteed uniform distribution of the returned elements. For more information about the algorithms used for SPOP, look up both the Knuth sampling and Floyd sampling algorithms.