 Usage:

ZRANGEBYSCORE key min max [ withscores ] [ LIMIT offset count ]
 Complexity:
 O(log(N)+M) with N being the number of elements in the sorted set and M the number of elements being returned. If M is constant (e.g. always asking for the first 10 elements with LIMIT), you can consider it O(log(N)).
 Since:
 1.0.5
Returns all the elements in the sorted set at key
with a score between min
and max
(including elements with score equal to min
or max
).
The elements are considered to be ordered from low to high scores.
The elements having the same score are returned in lexicographical order (this follows from a property of the sorted set implementation in Valkey and does not involve further computation).
The optional LIMIT
argument can be used to only get a range of the matching
elements (similar to SELECT LIMIT offset, count in SQL). A negative count
returns all elements from the offset
.
Keep in mind that if offset
is large, the sorted set needs to be traversed for
offset
elements before getting to the elements to return, which can add up to
O(N) time complexity.
The optional WITHSCORES
argument makes the command return both the element and
its score, instead of the element alone.
Exclusive intervals and infinity
min
and max
can be inf
and +inf
, so that you are not required to know
the highest or lowest score in the sorted set to get all elements from or up to
a certain score.
By default, the interval specified by min
and max
is closed (inclusive).
It is possible to specify an open interval (exclusive) by prefixing the score
with the character (
.
For example:
ZRANGEBYSCORE zset (1 5
Will return all elements with 1 < score <= 5
while:
ZRANGEBYSCORE zset (5 (10
Will return all the elements with 5 < score < 10
(5 and 10 excluded).
Examples
127.0.0.1:6379> ZADD myzset 1 "one"
(integer) 1
127.0.0.1:6379> ZADD myzset 2 "two"
(integer) 1
127.0.0.1:6379> ZADD myzset 3 "three"
(integer) 1
127.0.0.1:6379> ZRANGEBYSCORE myzset inf +inf
1) "one"
2) "two"
3) "three"
127.0.0.1:6379> ZRANGEBYSCORE myzset 1 2
1) "one"
2) "two"
127.0.0.1:6379> ZRANGEBYSCORE myzset (1 2
1) "two"
127.0.0.1:6379> ZRANGEBYSCORE myzset (1 (2
(empty array)
Pattern: weighted random selection of an element
Normally ZRANGEBYSCORE
is simply used in order to get range of items
where the score is the indexed integer key, however it is possible to do less
obvious things with the command.
For example a common problem when implementing Markov chains and other algorithms is to select an element at random from a set, but different elements may have different weights that change how likely it is they are picked.
This is how we use this command in order to mount such an algorithm:
Imagine you have elements A, B and C with weights 1, 2 and 3. You compute the sum of the weights, which is 1+2+3 = 6
At this point you add all the elements into a sorted set using this algorithm:
SUM = ELEMENTS.TOTAL_WEIGHT // 6 in this case.
SCORE = 0
FOREACH ELE in ELEMENTS
SCORE += ELE.weight / SUM
ZADD KEY SCORE ELE
END
This means that you set:
A to score 0.16
B to score .5
C to score 1
Since this involves approximations, in order to avoid C is set to, like, 0.998 instead of 1, we just modify the above algorithm to make sure the last score is 1 (left as an exercise for the reader...).
At this point, each time you want to get a weighted random element,
just compute a random number between 0 and 1 (which is like calling
rand()
in most languages), so you can just do:
RANDOM_ELE = ZRANGEBYSCORE key RAND() +inf LIMIT 0 1
History
Version  Change 

2.0.0  Added the 