ContextQMD
Back to Redis

VRANDMEMBER

content/commands/vrandmember.md

latest3.4 KB
Original Source

Return one or more random elements from a vector set.

The behavior is similar to the SRANDMEMBER command:

  • When called without a count, returns a single element as a bulk string.
  • When called with a positive count, returns up to that many distinct elements (no duplicates).
  • When called with a negative count, returns that many elements, possibly with duplicates.
  • If the count exceeds the number of elements, the entire set is returned.
  • If the key does not exist, the command returns null if no count is given, or an empty array if a count is provided.
shell
VADD vset VALUES 3 1 0 0 elem1
VADD vset VALUES 3 0 1 0 elem2
VADD vset VALUES 3 0 0 1 elem3

Return a single random element:

shell
VRANDMEMBER vset
"elem2"

Return two distinct random elements:

shell
VRANDMEMBER vset 2
1) "elem1"
2) "elem3"

Return 3 random elements with possible duplicates:

shell
VRANDMEMBER vset -3
1) "elem2"
2) "elem2"
3) "elem1"

Request more elements than exist in the set:

shell
VRANDMEMBER vset 10
1) "elem1"
2) "elem2"
3) "elem3"

When the key doesn't exist:

shell
VRANDMEMBER nonexistent
(nil)
shell
VRANDMEMBER nonexistent 3
(empty array)

This command is useful for:

  • Sampling elements for testing or training.
  • Generating random queries for performance testing.

Internally:

  • For small counts (less than 20% of the set size), a dictionary is used to ensure uniqueness.
  • For large counts (more than 20% of the set size), a linear scan provides faster performance, though results may be less random.

Required arguments

<details open> <summary><code>key</code></summary>

is the name of the key that holds the vector set.

</details>

Optional arguments

<details open> <summary><code>count</code></summary>

specifies the number of elements to return. Positive values return distinct elements; negative values allow duplicates.

</details>
  • [Vector sets]({{< relref "/develop/data-types/vector-sets" >}})

Redis Software and Redis Cloud compatibility

| Redis Software | Redis Cloud | <span style="min-width: 9em; display: table-cell">Notes</span> | |:----------------------|:-----------------|:------| | <span title="Supported">✅ Standard</span> <span title="Not supported"><nobr>❌ Active-Active</nobr></span> | <span title="Supported">✅ Standard</span> <span title="Not supported"><nobr>❌ Active-Active</nobr></span> | |

Return information

{{< multitabs id="vrandmember-return-info" tab1="RESP2" tab2="RESP3" >}}

One of the following:

-tab-sep-

One of the following:

{{< /multitabs >}}