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DiceDB

SCARD

The SCARD command in DiceDB is used to get the number of members in a set. This command is useful for determining the size of a set stored at a given key.

Syntax

Terminal window
SCARD key

Parameters

ParameterDescriptionTypeRequired
keyThe key of the set whose cardinality (number of members) you want to retrieve.StringYes

Return Values

ConditionReturn Value
Key of Set type existsNumber of elements in the set
Key doesn’t exist0
Invalid syntax/key is of the wrong typeerror

Behaviour

When the SCARD command is executed, DiceDB will:

  1. Check if the key exists.
  2. If the key exists and is a set, it will return the number of elements in the set.
  3. If the key does not exist, it will return 0.
  4. If the key exists but is not a set, an error will be returned.

Errors

  1. Wrong type of key:

    • Error Message: (error) ERROR WRONGTYPE Operation against a key holding the wrong kind of value
    • Occurs if the key exists but is not a set. DiceDB expects the key to be associated with a set data type. If the key is associated with a different data type (e.g., a string, list, hash, or sorted set), this error will be raised.

  2. Wrong number of arguments:

    • Error Message: (error) ERROR wrong number of arguments for 'scard' command
    • Occurs if wrong number of keys is passed to the command, such as passing more than 1 key, or passing no key.

Examples

Basic Example

Add three members to the set myset and then get the cardinality of the set using SCARD command.

Terminal window
127.0.0.1:7379> SADD myset "apple"
(integer) 1
127.0.0.1:7379> SADD myset "banana"
(integer) 1
127.0.0.1:7379> SADD myset "cherry"
(integer) 1
127.0.0.1:7379> SCARD myset
(integer) 3

Non-Existent Key

Get the cardinality of a set that does not exist.

Terminal window
127.0.0.1:7379> SCARD nonexistingset
(integer) 0

Error Example: Wrong Type

Get the cardinality of a key holding string value

Terminal window
127.0.0.1:7379> SET mystring "hello"
OK
127.0.0.1:7379> SCARD mystring
(error) ERROR WRONGTYPE Operation against a key holding the wrong kind of value

Error Example: Wrong Argument

Get cardinality of a set holding 0 or more than 1 argument

Terminal window
127.0.0.1:7379> SCARD
(error) ERROR wrong number of arguments for 'scard' command
127.0.0.1:7379> SCARD myset1 myset2
(error) ERROR wrong number of arguments for 'scard' command