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DiceDB

ZPOPMAX

The ZPOPMAX command in DiceDB is used to remove and return the members with the highest scores from the sorted set data structure at the specified key. The second argument count is optional which specifies the number of elements that needs to be popped from the sorted set.

Syntax

Terminal window
ZPOPMAX key [count]

Parameters

ParameterDescriptionTypeRequired
keyThe name of the sorted set data structure. If it does not exist, an empty array is returned.StringYes
countThe count argument specifies the maximum number of members to return from highest to lowest.IntegerNo

Return values

ConditionReturn Value
If the key is of valid type and records are presentList of members including their scores
If the key does not exist or if the sorted set is empty(empty list or set)

Behaviour

  • The command first checks if the specified key exists.
  • If the key does not exist, an empty array is returned.
  • If the key exists but is not a sorted set, an error is returned.
  • If the count argument is specified, up to that number of members with the highest scores are returned and removed.
  • The returned array contains the members and their corresponding scores in the order of highest to lowest.

Errors

  1. Wrong type error:

    • Error Message: (error) WRONGTYPE Operation against a key holding the wrong kind of value
    • Occurs when trying to use the command on a key that is not a sorted set.

  2. Syntax error:

    • Error Message: (error) ERROR wrong number of arguments for 'zpopMAX' command
    • Occurs when the command syntax is incorrect or missing required parameters.

  3. Invalid argument type error:

    • Error Message : (error) ERR value is not an integer or out of range
    • Occurs when the count argument passed to the command is not an integer.

Examples

Non-Existing Key (without count argument)

Attempting to pop the member with the highest score from a non-existent sorted set:

Terminal window
127.0.0.1:7379> ZPOPMAX NON_EXISTENT_KEY
(empty array)

Existing Key (without count argument)

Popping the member with the highest score from an existing sorted set:

Terminal window
127.0.0.1:7379> ZADD myzset 1 member1 2 member2 3 member3
(integer) 3
127.0.0.1:7379> ZPOPMAX myzset
1) 1 "member1"

With Count Argument

Popping multiple members with the highest scores using the count argument:

Terminal window
127.0.0.1:7379> ZADD myzset 1 member1 2 member2 3 member3
(integer) 3
127.0.0.1:7379> ZPOPMAX myzset 2
1) 1 "member1"
2) 2 "member2"

Count Argument but Multiple Members Have the Same Score

Popping members when multiple members share the same score:

Terminal window
127.0.0.1:7379> ZADD myzset 1 member1 1 member2 1 member3
(integer) 3
127.0.0.1:7379> ZPOPMAX myzset 2
1) 1 "member1"
2) 1 "member2"

Negative Count Argument

Attempting to pop members using a negative count argument:

Terminal window
127.0.0.1:7379> ZADD myzset 1 member1 2 member2 3 member3
(integer) 3
127.0.0.1:7379> ZPOPMAX myzset -1
(empty array)

Floating-Point Scores

Popping members with floating-point scores:

Terminal window
127.0.0.1:7379> ZADD myzset 1.5 member1 2.7 member2 3.8 member3
(integer) 3
127.0.0.1:7379> ZPOPMAX myzset
1) 1.5 "member1"

Wrong number of arguments

Attempting to pop from a key that is not a sorted set:

Terminal window
127.0.0.1:7379> SET stringkey "string_value"
OK
127.0.0.1:7379> ZPOPMAX stringkey
(error) WRONGTYPE Operation against a key holding the wrong kind of value

Invalid Count Argument

Using an invalid (non-integer) count argument:

Terminal window
127.0.0.1:7379> ZADD myzset 1 member1
(integer) 1
127.0.0.1:7379> ZPOPMAX myzset INCORRECT_COUNT_ARGUMENT
(error) ERR value is not an integer or out of range

Wrong Type of Key (without count argument)

Attempting to pop from a key that is not a sorted set:

Terminal window
127.0.0.1:7379> SET stringkey "string_value"
OK
127.0.0.1:7379> ZPOPMAX stringkey
(error) WRONGTYPE Operation against a key holding the wrong kind of value