$cardinality

$cardinality returns the number of distinct values in a field.

All matching field values are deduplicated, then counted.

If missing is provided, documents without the field are treated as that fallback key (which can increase the distinct count by at most one extra value).

Compatibility

Field Type	Supported
TEXT	No
U64/I64/F64	Yes
DATE	Yes
BOOL	Yes
KEYWORD	Yes
FACET	No

Field must be FAST.

Arguments

Argument	Type	Required	Description
field	string	Yes	Field to aggregate.
missing	string | number	No	Fallback key for missing fields.

TypeScript

await index.aggregate({
  aggregations: {
    unique_users: { $cardinality: { field: "userId" } },
  },
});

Python

index.aggregate(
    aggregations={"unique_users": {"$cardinality": {"field": "userId"}}}
)

Redis CLI

SEARCH.AGGREGATE events '{}' '{"unique_users": {"$cardinality": {"field": "userId"}}}'

Output

{ "unique_categories": { "value": 3 } }