LLEN

The LLEN command in DiceDB is used to obtain the length of a list stored at a specified key. This command is particularly useful for determining the number of elements in a list, which can help in various list management and processing tasks.

Syntax

LLEN key

Parameters

Parameter	Description	Type	Required
key	The key associated with the list whose length you want to retrieve.	String	Yes

Return values

Condition	Return Value
Command is successful	Integer denoting the length of the list at the specified key.
If the key does not exist	0 (the key is interpreted as an empty list)
Syntax or specified constraints are invalid	error

Behaviour

• If the key exists and is associated with a list, the LLEN command returns the number of elements in the list.
• If the key does not exist, the LLEN command returns 0, indicating that the list is empty.
• If the key exists but is not associated with a list, an error is returned.

Errors

1. Wrong type of value or key:

   • Error Message: (error) WRONGTYPE Operation against a key holding the wrong kind of value
   • Occurs if the key exists but is not associated with a list.

2. Wrong number of arguments

   • Error Message: (error) ERR wrong number of arguments for 'llen' command
   • Occurs if command is executed without any arguments or with 2 or more arguments

Example Usage

Basic Usage

Getting the LLEN of a list mylist with values ["one", "two", "three"].

127.0.0.1:7379> RPUSH mylist "one"
(integer) 1
127.0.0.1:7379> RPUSH mylist "two"
(integer) 2
127.0.0.1:7379> RPUSH mylist "three"
(integer) 3
127.0.0.1:7379> LLEN mylist
(integer) 3

Non-Existent Key

Getting the LLEN of a list nonExistentList which does not exist.

127.0.0.1:7379> LLEN nonExistentList
(integer) 0

Invalid Usage: Key is Not a List

Trying to get the LLEN of a key mystring which is holding wrong data type string.

127.0.0.1:7379> SET mystring "Hello, World!"
OK
127.0.0.1:7379> LLEN mystring
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Best Practices

• Check Key Type: Before using LLEN, ensure that the key is associated with a list to avoid errors.
• Handle Non-Existent Keys: Be prepared to handle the case where the key does not exist, as LLEN will return 0 in such scenarios.
• Use in Conjunction with Other List Commands: The LLEN command is often used alongside other list commands like RPUSH, LPUSH, LPOP, and RPOP to manage and process lists effectively.