Redis provides us with two commands that allow us to get one or more random members from a given set – SRANDMEMBER and SPOP.

Actually, the commands are slightly different in that one deletes the random member whereas the other doesn’t, and so the command you choose will depend on whether or not you want to delete the random member at the same time.

The SRANDMEMBER Command

The SRANDMEMBER command returns one or more random members from a specified set. It doesn’t delete the member/s like SPOP does.

Suppose we have the following set:

SMEMBERS animals

Result:

1) "Horse"
2) "Dog"
3) "Cat"
4) "Cow"
5) "Bird"
6) "Zebra"

We can use SRANDMEMBER to return a random member from that set:

SRANDMEMBER animals

Result:

"Zebra"

And when we run it again, another random member is returned:

SRANDMEMBER animals

Result:

"Dog"

We can also pass a second argument to specify how many random members to return:

SRANDMEMBER animals 3

Result:

1) "Horse"
2) "Dog"
3) "Bird"

By default, SRANDMEMBER returns distinct values, but we can also pass a negative count value to return non-distinct members from the set. When we do this, the number of members returned is the absolute value of the negative value.

Example:

SRANDMEMBER animals -3

Result:

1) "Bird"
2) "Horse"
3) "Horse"

This doesn’t mean that it will always return distinct values, but the negative count value ensures that non-distinct values can be returned.

The SPOP Command

The SPOP command returns one or more random members from a specified set, and deletes those members.

Here’s an example:

SPOP animals

Result:

"Horse"

Now if we check the contents of the animals set, we’ll see that it no longer contains Horse:

SMEMBERS animals

Result:

1) "Cow"
2) "Cat"
3) "Bird"
4) "Dog"
5) "Zebra"

We can pass a count argument to determine how many random members are removed and returned:

SPOP animals 2

Result:

1) "Cow"
2) "Dog"

Now when we check the set’s contents, we see that it no longer contains those two members:

SMEMBERS animals

Result:

1) "Cat"
2) "Bird"
3) "Zebra"