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Sorted sets are collections of unique strings ordered by an associated score. Each member has a floating-point score that determines its position in the set. Kora implements all standard Redis sorted set operations with identical semantics.

​
ZADD

Add one or more members to a sorted set, or update scores if they already exist. Syntax 
ZADD key score member [score member ...]
​
key
string
required
The key of the sorted set
​
score
float
required
The score associated with the member (used for ordering)
​
member
string
required
One or more members to add
Return value
​
count
integer
The number of members added to the sorted set (excluding score updates to existing members)
Examples 
redis-cli> ZADD leaderboard 100 "alice"
(integer) 1
redis-cli> ZADD leaderboard 85 "bob" 92 "charlie"
(integer) 2
redis-cli> ZADD leaderboard 95 "alice"
(integer) 0
redis-cli> ZRANGE leaderboard 0 -1 WITHSCORES
1) "bob"
2) "85"
3) "charlie"
4) "92"
5) "alice"
6) "95"
Time complexity: O(log(N)) for each item added, where N is the number of elements in the sorted set Implementation details: Kora stores sorted sets as a HashMap mapping members to scores, maintaining efficient lookups while providing sorted access through on-demand sorting operations.

​
ZREM

Remove one or more members from a sorted set. Syntax 
ZREM key member [member ...]
​
key
string
required
The key of the sorted set
​
member
string
required
One or more members to remove
Return value
​
count
integer
The number of members removed from the sorted set
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZREM myzset "two"
(integer) 1
redis-cli> ZRANGE myzset 0 -1 WITHSCORES
1) "one"
2) "1"
3) "three"
4) "3"
Time complexity: O(M*log(N)) where N is the number of elements in the sorted set and M is the number of elements removed

​
ZSCORE

Get the score associated with a member in a sorted set. Syntax 
ZSCORE key member
​
key
string
required
The key of the sorted set
​
member
string
required
The member to query
Return value
​
score
string | null
The score of the member (as a string), or null if the member does not exist
Examples 
redis-cli> ZADD myzset 1.5 "one"
(integer) 1
redis-cli> ZSCORE myzset "one"
"1.5"
redis-cli> ZSCORE myzset "two"
(nil)
Time complexity: O(1)

​
ZRANK

Get the rank (index) of a member in a sorted set, ordered from low to high scores. Syntax 
ZRANK key member
​
key
string
required
The key of the sorted set
​
member
string
required
The member to query
Return value
​
rank
integer | null
The rank of the member (0-based), or null if the member does not exist
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZRANK myzset "three"
(integer) 2
redis-cli> ZRANK myzset "one"
(integer) 0
redis-cli> ZRANK myzset "four"
(nil)
Time complexity: O(N) where N is the number of elements in the sorted set Implementation details: Kora computes rank by sorting the entire set and finding the position. Members with equal scores are ordered lexicographically.

​
ZREVRANK

Get the rank (index) of a member in a sorted set, ordered from high to low scores. Syntax 
ZREVRANK key member
​
key
string
required
The key of the sorted set
​
member
string
required
The member to query
Return value
​
rank
integer | null
The reverse rank of the member (0-based), or null if the member does not exist
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZREVRANK myzset "one"
(integer) 2
redis-cli> ZREVRANK myzset "three"
(integer) 0
Time complexity: O(N) where N is the number of elements in the sorted set

​
ZCARD

Get the number of members in a sorted set. Syntax 
ZCARD key
​
key
string
required
The key of the sorted set
Return value
​
cardinality
integer
The number of members in the sorted set, or 0 if the key does not exist
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two"
(integer) 2
redis-cli> ZCARD myzset
(integer) 2
Time complexity: O(1)

​
ZCOUNT

Count the members in a sorted set with scores within a given range. Syntax 
ZCOUNT key min max
​
key
string
required
The key of the sorted set
​
min
float
required
Minimum score (inclusive)
​
max
float
required
Maximum score (inclusive)
Return value
​
count
integer
The number of members with scores in the specified range
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZCOUNT myzset -inf +inf
(integer) 3
redis-cli> ZCOUNT myzset 1 2
(integer) 2
Time complexity: O(N) where N is the number of elements in the sorted set

​
ZINCRBY

Increment the score of a member in a sorted set. Syntax 
ZINCRBY key increment member
​
key
string
required
The key of the sorted set
​
increment
float
required
The amount to increment (can be negative)
​
member
string
required
The member whose score to increment
Return value
​
score
string
The new score of the member after incrementing
Examples 
redis-cli> ZADD myzset 1 "one"
(integer) 1
redis-cli> ZINCRBY myzset 2 "one"
"3"
redis-cli> ZINCRBY myzset -1 "one"
"2"
redis-cli> ZINCRBY myzset 5 "two"
"5"
Time complexity: O(log(N)) where N is the number of elements in the sorted set Implementation details: If the member does not exist, it is created with an initial score of 0 before applying the increment.

​
ZLEXCOUNT

Count the members in a sorted set within a lexicographical range. Syntax 
ZLEXCOUNT key min max
​
key
string
required
The key of the sorted set
​
min
string
required
Minimum lexicographical value. Use - for negative infinity, [value for inclusive, (value for exclusive
​
max
string
required
Maximum lexicographical value. Use + for positive infinity, [value for inclusive, (value for exclusive
Return value
​
count
integer
The number of members in the specified lexicographical range
Examples 
redis-cli> ZADD myzset 0 "a" 0 "b" 0 "c" 0 "d" 0 "e"
(integer) 5
redis-cli> ZLEXCOUNT myzset - +
(integer) 5
redis-cli> ZLEXCOUNT myzset [b [d
(integer) 3
Time complexity: O(N) where N is the number of elements in the sorted set Implementation details: This command is useful when all members have the same score and you want to perform range queries by member name.

​
ZMSCORE

Get the scores of multiple members in a sorted set. Syntax 
ZMSCORE key member [member ...]
​
key
string
required
The key of the sorted set
​
member
string
required
One or more members to query
Return value
​
scores
array
Array of scores (as strings) or null values, one for each member in the same order
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two"
(integer) 2
redis-cli> ZMSCORE myzset "one" "two" "three"
1) "1"
2) "2"
3) (nil)
Time complexity: O(N) where N is the number of members being looked up

​
ZPOPMAX

Remove and return members with the highest scores in a sorted set. Syntax 
ZPOPMAX key [count]
​
key
string
required
The key of the sorted set
​
count
integer
Number of members to pop (default: 1)
Return value
​
members
array
Array of member-score pairs (member, score, member, score, …) for the popped elements
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZPOPMAX myzset
1) "three"
2) "3"
redis-cli> ZPOPMAX myzset 2
1) "two"
2) "2"
3) "one"
4) "1"
Time complexity: O(N*log(M)) where N is the number of elements to pop and M is the number of elements in the sorted set

​
ZPOPMIN

Remove and return members with the lowest scores in a sorted set. Syntax 
ZPOPMIN key [count]
​
key
string
required
The key of the sorted set
​
count
integer
Number of members to pop (default: 1)
Return value
​
members
array
Array of member-score pairs (member, score, member, score, …) for the popped elements
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZPOPMIN myzset
1) "one"
2) "1"
redis-cli> ZPOPMIN myzset 2
1) "two"
2) "2"
3) "three"
4) "3"
Time complexity: O(N*log(M)) where N is the number of elements to pop and M is the number of elements in the sorted set

​
ZRANDMEMBER

Get one or multiple random members from a sorted set. Syntax 
ZRANDMEMBER key [count [WITHSCORES]]
​
key
string
required
The key of the sorted set
​
count
integer
Number of members to return. Positive values return distinct members, negative values allow duplicates
​
WITHSCORES
Include scores in the output
Return value
​
members
string | array | null
Without count: a single random member, or null if empty. With count: array of members (and scores if WITHSCORES)
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZRANDMEMBER myzset
"two"
redis-cli> ZRANDMEMBER myzset 2 WITHSCORES
1) "one"
2) "1"
3) "three"
4) "3"
redis-cli> ZRANDMEMBER myzset -5
1) "one"
2) "two"
3) "one"
4) "three"
5) "two"
Time complexity: O(N) where N is the number of members returned

​
ZRANGE

Return a range of members in a sorted set by index. Syntax 
ZRANGE key start stop [WITHSCORES]
​
key
string
required
The key of the sorted set
​
start
integer
required
Start index (0-based, negative values count from the end)
​
stop
integer
required
Stop index (inclusive, negative values count from the end)
​
WITHSCORES
Include scores in the output
Return value
​
members
array
Array of members (and scores if WITHSCORES) in the specified range, ordered by score ascending
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZRANGE myzset 0 -1
1) "one"
2) "two"
3) "three"
redis-cli> ZRANGE myzset 0 1 WITHSCORES
1) "one"
2) "1"
3) "two"
4) "2"
redis-cli> ZRANGE myzset -2 -1
1) "two"
2) "three"
Time complexity: O(log(N)+M) where N is the number of elements in the sorted set and M is the number of elements returned Implementation details: Members with equal scores are ordered lexicographically.

​
ZRANGEBYLEX

Return a range of members in a sorted set by lexicographical order. Syntax 
ZRANGEBYLEX key min max [LIMIT offset count]
​
key
string
required
The key of the sorted set
​
min
string
required
Minimum value. Use - for negative infinity, [value for inclusive, (value for exclusive
​
max
string
required
Maximum value. Use + for positive infinity, [value for inclusive, (value for exclusive
​
LIMIT
Optional offset and count to limit results
Return value
​
members
array
Array of members in the specified lexicographical range
Examples 
redis-cli> ZADD myzset 0 "a" 0 "b" 0 "c" 0 "d" 0 "e"
(integer) 5
redis-cli> ZRANGEBYLEX myzset - [c
1) "a"
2) "b"
3) "c"
redis-cli> ZRANGEBYLEX myzset [aaa (g
1) "b"
2) "c"
3) "d"
4) "e"
redis-cli> ZRANGEBYLEX myzset - + LIMIT 2 2
1) "c"
2) "d"
Time complexity: O(log(N)+M) where N is the number of elements in the sorted set and M is the number of elements returned

​
ZRANGEBYSCORE

Return a range of members in a sorted set by score. Syntax 
ZRANGEBYSCORE key min max [WITHSCORES] [LIMIT offset count]
​
key
string
required
The key of the sorted set
​
min
float
required
Minimum score (inclusive)
​
max
float
required
Maximum score (inclusive)
​
WITHSCORES
Include scores in the output
​
LIMIT
Optional offset and count to limit results
Return value
​
members
array
Array of members (and scores if WITHSCORES) with scores in the specified range, ordered by score ascending
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZRANGEBYSCORE myzset -inf +inf
1) "one"
2) "two"
3) "three"
redis-cli> ZRANGEBYSCORE myzset 1 2
1) "one"
2) "two"
redis-cli> ZRANGEBYSCORE myzset 1 2 WITHSCORES
1) "one"
2) "1"
3) "two"
4) "2"
redis-cli> ZRANGEBYSCORE myzset 0 10 LIMIT 1 2
1) "two"
2) "three"
Time complexity: O(log(N)+M) where N is the number of elements in the sorted set and M is the number of elements returned

​
ZREVRANGE

Return a range of members in a sorted set by index, with scores ordered from high to low. Syntax 
ZREVRANGE key start stop [WITHSCORES]
​
key
string
required
The key of the sorted set
​
start
integer
required
Start index (0-based, negative values count from the end)
​
stop
integer
required
Stop index (inclusive, negative values count from the end)
​
WITHSCORES
Include scores in the output
Return value
​
members
array
Array of members (and scores if WITHSCORES) in the specified range, ordered by score descending
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZREVRANGE myzset 0 -1
1) "three"
2) "two"
3) "one"
redis-cli> ZREVRANGE myzset 0 1 WITHSCORES
1) "three"
2) "3"
3) "two"
4) "2"
Time complexity: O(log(N)+M) where N is the number of elements in the sorted set and M is the number of elements returned

​
ZREVRANGEBYLEX

Return a range of members in a sorted set by lexicographical order, in reverse. Syntax 
ZREVRANGEBYLEX key max min [LIMIT offset count]
​
key
string
required
The key of the sorted set
​
max
string
required
Maximum value. Use + for positive infinity, [value for inclusive, (value for exclusive
​
min
string
required
Minimum value. Use - for negative infinity, [value for inclusive, (value for exclusive
​
LIMIT
Optional offset and count to limit results
Return value
​
members
array
Array of members in the specified lexicographical range, in reverse order
Examples 
redis-cli> ZADD myzset 0 "a" 0 "b" 0 "c" 0 "d" 0 "e"
(integer) 5
redis-cli> ZREVRANGEBYLEX myzset [c -
1) "c"
2) "b"
3) "a"
redis-cli> ZREVRANGEBYLEX myzset (g [aaa
1) "e"
2) "d"
3) "c"
4) "b"
Time complexity: O(log(N)+M) where N is the number of elements in the sorted set and M is the number of elements returned

​
ZREVRANGEBYSCORE

Return a range of members in a sorted set by score, with scores ordered from high to low. Syntax 
ZREVRANGEBYSCORE key max min [WITHSCORES] [LIMIT offset count]
​
key
string
required
The key of the sorted set
​
max
float
required
Maximum score (inclusive)
​
min
float
required
Minimum score (inclusive)
​
WITHSCORES
Include scores in the output
​
LIMIT
Optional offset and count to limit results
Return value
​
members
array
Array of members (and scores if WITHSCORES) with scores in the specified range, ordered by score descending
Examples 
redis-cli> ZADD myzset 1 "one" 2 "two" 3 "three"
(integer) 3
redis-cli> ZREVRANGEBYSCORE myzset +inf -inf
1) "three"
2) "two"
3) "one"
redis-cli> ZREVRANGEBYSCORE myzset 2 1
1) "two"
2) "one"
redis-cli> ZREVRANGEBYSCORE myzset 2 1 WITHSCORES
1) "two"
2) "2"
3) "one"
4) "1"
redis-cli> ZREVRANGEBYSCORE myzset 10 0 LIMIT 1 2
1) "two"
2) "one"
Time complexity: O(log(N)+M) where N is the number of elements in the sorted set and M is the number of elements returned

​
ZSCAN

Incrementally iterate sorted set members and their scores. Syntax 
ZSCAN key cursor [MATCH pattern] [COUNT count]
​
key
string
required
The key of the sorted set
​
cursor
integer
required
The cursor position (use 0 to start)
​
MATCH
string
Glob pattern to filter members
​
COUNT
integer
Hint for how many members to return
Return value
​
result
array
Array with two elements: [0] next cursor, [1] array of member-score pairs
Examples 
redis-cli> ZADD myzset 1 "a" 2 "b" 3 "c" 4 "d" 5 "e" 6 "f"
(integer) 6
redis-cli> ZSCAN myzset 0 MATCH a* COUNT 5
1) "0"
2) 1) "a"
   2) "1"
redis-cli> ZSCAN myzset 0 COUNT 3
1) "3"
2) 1) "a"
   2) "1"
   3) "b"
   4) "2"
   5) "c"
   6) "3"
Time complexity: O(1) for every call, O(N) for a complete iteration Implementation details: The cursor is an offset into a lexicographically sorted list of members. When the returned cursor is 0, the iteration is complete.

​
Redis Compatibility

Kora implements all standard Redis sorted set commands with identical semantics. Sorted sets are stored using a HashMap for efficient score lookups, with sorting performed on-demand for range queries. Members with equal scores are ordered lexicographically for consistent ordering.

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