LRANGE

The LRANGE command in DiceDB returns the specified elements of the list stored at key.

The offsets start and stop are zero-based indexes, with 0 being the first element of the list (the head of the list), 1 being the next element and so on.

These offsets can also be negative numbers indicating offsets starting at the end of the list. For example, -1 is the last element of the list, -2 the penultimate, and so on.

Out of range indexes will not produce an error. If start is larger than the end of the list, an empty list is returned. If stop is larger than the actual end of the list it will be treated like the last element of the list.

Syntax

LRANGE key start stop

Parameters

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

Return values

Condition	Return Value
Command is successful	Array reply: a list of elements in the specified range
If the key does not exist	An empty array if the key doesn’t exist.
Syntax or specified constraints are invalid	error

Behaviour

• If the key exists and is associated with a list, the LRANGE command returns the specified elements of the list stored at key.
• If the key does not exist, the LRANGE command returns an empty array.
• 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) wrong number of arguments for LRANGE
   • Occurs when invalid arguments are passed to the command.

3. Invalid start or stop offsets:

   • Error Message: (error) ERR value is not an integer or out of range
   • Occurs when the start/stop offset is not valid.

Example Usage

Basic Usage

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

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> LRANGE mylist 0 100
1) "one"
2) "two"
127.0.0.1:7379> LRANGE mylist -1 10
1) "two"

Non-Existent Key

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

127.0.0.1:7379> LRANGE nonexistentlist 0 100
(empty array)

Invalid start/stop offset

Trying to get the LRANGE on a key mylist with invalid stop offset.

127.0.0.1:7379> LRANGE mylist 0 10ff
(error) ERR value is not an integer or out of range

Invalid usage

Trying to get the LRANGE on a key myhash which doens’t hold list data type.

127.0.0.1:7379> HMSET myhash field1 "value1"
OK
127.0.0.1:7379> HGET myhash field1
"value1"
127.0.0.1:7379> LRANGE myhash 0 100
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Best Practices

• Check Key Type: Before using LRANGE, 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 LRANGE will return an empty array in such scenarios.
• Use in Conjunction with Other List Commands: The LRANGE command is often used alongside other list commands like RPUSH, LPUSH, LPOP, and RPOP to manage and process lists effectively.