RPOP

The RPOP command in DiceDB is used to remove and return the last element of a list. This command is useful when processing elements in a Last-In-First-Out (LIFO) order.

Syntax

RPOP key

Parameters

Parameter	Description	Type	Required
key	The key of the list from which the last element will be removed.	String	Yes

Return values

Condition	Return Value
The command is successful	String The value of the last element in the list
The key does not exist	nil
The key is of the wrong type	error

Behaviour

• When the RPOP command is executed, DiceDB checks if the key exists and is associated with a list.
• If the list has elements, the last element is removed and returned.
• If the key does not exist, the command treats it as an empty list and returns nil.
• If the key exists but is not associated with a list, a WRONGTYPE error is returned.
• If more than one key is passed, 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 'lpop' command
   • Occurs if command is executed without any arguments or with 2 or more arguments

Example Usage

Basic Usage

127.0.0.1:7379> LPUSH mylist "one" "two" "three"
(integer) 3
127.0.0.1:7379> RPOP mylist
"one"

Non-Existent Key

Returns (nil) if the provided key is non-existent

127.0.0.1:7379> RPOP emptylist
(nil)

Invalid Usage: Key is Not a List

Trying to LPOP a key mystring which is holding wrong data type string.

SET mystring "hello"
OK
LPOP mystring
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Invalid Usage: Wrong Number of Arguments

Passing more than one key will result in an error:

RPOP mylist secondlist
(error) ERR wrong number of arguments for 'lpop' command

Best Practices

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

By understanding the RPOP command, you can effectively manage lists in DiceDB, ensuring that you can retrieve and process elements in a LIFO order.