Complete tutorial on Sorted Sets in Redis

Sorted sets are sets with some additional functionalities that is they can be sorted in some ways, allowing more control over the data that is stored in sets. Sorted sets maintain an ordered collection of unique elements, associated with scores (unique no).

Some of the best use cases of it are making a leaderboard, ranking systems, etc. Its actual Data structure is a combination of a list and hash table having characteristics of both sets and sorted lists. These sorted sets contain a unique score that allows the elements to be sorted in ascending or descending order.

Syntax and Commands of Redis Sorted Sets

1. “zadd” command:

Makes a sorted set, and adds elements to it

Syntax: zadd set_name Core_no. Value

Example: zadd Users 1 Amisha 2 Abhinav 3 Vijay

Explanation: We made a sorted set namely “Users” in which we added 3 elements “Amisha”, “Abhinav” and “Vijay”. We assigned these elements a Unique no./Core no. as 1, 2 and 3. Must note that Core no. are not index no.

Output:

2. “zrange” command:

Shows the elements present in sorted set according to the range you specify

Syntax: zrange set_name range_in_integer

Example: zrange Users 0 -1 (Shows the elements of the users_set from 0 to -1)

Explaination: Shows the elements of set “Users”, 0 -1 indicating all elements. If we write 0 1, then it will show “Amisha” and “Abhinav” only.

Output:

3. “zrange” command (zrange command with Core no.):

Syntax: zrange set_name range_integer withscores

Example: zrange Users 0 -1 withscores

Explanation: Shows the elements with core no. also

Output:

4. “zcard” command:

Shows length of sorted set

Syntax: zcard set_name

Example: zcard Users

Explanation: Counts no. of elements of set and displays total no. of elements

Output:

5. “zcount” command:

Counts no of elements

Syntax: zcount set_name range

Example: zcount Users -inf +inf

Explaination: -infinity to +infinity for all values

Output:

6. “zcount” command (Counts elements with their core no.):

Syntax: zcount set_name Core_no.

Example: zcount Users 0 2

Explanation: All elements in Users set with having Core no. 0 to 2 are displayed

Output:

7. “zrem” command:

Removes an element from the set

Syntax: zrem set_name element_name

Example: zrem Users Vijay

Explanation: Vijay will be removed from the Users set

Output:

8. “zrevrange” command:

Reverses the elements in the set

Syntax: zrevrange set_name range withscores

Example: zrevrange Users 0 -1 withscores

Explanation: Reverses the elements of the sorted set.

Output:

9. “zscore” command:

Returns Core no. of a particular element present in that set

Syntax: zscore set_name element_name

Example: zscore Users Abhinav

Explaination: Returns Core no. of element “Abhinav” which is “2”.

Output:

10. “zrevrangebyscore” command:

Reverses the list by core no.

Syntax: zrevrangebyscore set_name range withscores

Example: zrevrangebyscore Users 2 0 withscores

Explaination: Users set was reversed, and is getting displayed with Core no. as well.

Output:

11. “zremrangebyscore” command:

Removes the elements from set in particular Core no. range

Syntax: zremrangebyscore set_name core_no_range

Example: zremrangebyscore Users 0 2

Explaination: Removes the elements by core score from Users set

Output:

12. “zremrangebyrank” command:

Removes the elements by their index/rank

Syntax: zremrangebyrank set_name rank_range

Example: zremrangebyrank Users 0 2

Explaination: Removes the list by rank, hence the set is now empty

Output:

Performance of Sorted Sets in Redis:

Time Complexity of Sorted Sets operations is generally O(log(N)), where N is the number of members, but be careful while using the ZRANGE command with large number of return values because the time complexity of this command is O(log(N) + M), where M is the number of results returned by the command