zset

Introduction

zset provides a concurrent-safety sorted set, can be used as a local replacement of Redis' zset.

The main difference to other sets is, every value of set is associated with a score, that is used to take the sorted set ordered, from the smallest to the greatest score.

The zset has O(log(N)) time complexity when doing Add(ZADD) and Remove(ZREM) operations and O(1) time complexity when doing Contains operations.

Features

• Concurrent safe API
• Values are sorted with score
• Implementation equivalent to redis
• Fast skiplist level randomization

Comparison

Redis command	Go function
ZADD	Add
ZINCRBY	IncrBy
ZREM	Remove
ZREMRANGEBYSCORE	RemoveRangeByScore
ZREMRANGEBYRANK	RemoveRangeByRank
ZUNION	Union
ZINTER	Inter
ZINTERCARD	TODO
ZDIFF	TODO
ZRANGE	Range
ZRANGEBYSCORE	IncrBy
ZREVRANGEBYSCORE	RevRangeByScore
ZCOUNT	Count
ZREVRANGE	RevRange
ZCARD	Len
ZSCORE	Score
ZRANK	Rank
ZREVRANK	RevRank
ZPOPMIN	TODO
ZPOPMAX	TODO
ZRANDMEMBER	TODO

List of redis commands are generated from the following command:

cat redis/src/server.c | grep -o '"z.*",z.*Command' | grep -o '".*"' | cut -d '"' -f2

You may find that not all redis commands have corresponding go implementations, the reason is as follows:

Unsupported Commands

Redis' zset can operates elements in lexicographic order, which is not commonly used function, so zset does not support commands like ZREMRANGEBYLEX, ZLEXCOUNT and so on.

Redis command
ZREMRANGEBYLEX
ZRANGEBYLEX
ZREVRANGEBYLEX
ZLEXCOUNT

In redis, user accesses zset via a string key. We do not need such string key because we have variable. so the following commands are not implemented:

Redis command
ZUNIONSTORE
ZINTERSTORE
ZDIFFSTORE
ZRANGESTORE
ZMSCORE
ZSCAN

QuickStart

package main

import (
	"fmt"

	"github.com/bytedance/gopkg/collection/zset"
)

func main() {
	z := zset.NewFloat64()

	values := []string{"Alice", "Bob", "Zhang"}
	scores := []float64{90, 89, 59.9}
	for i := range values {
		z.Add(scores[i], values[i])
	}

	s, ok := z.Score("Alice")
	if ok {
		fmt.Println("Alice's score is", s)
	}

	n := z.Count(0, 60)
	fmt.Println("There are", n, "people below 60 points")

	for _, n := range z.Range(0, -1) {
		fmt.Println("zset range found", n.Value, n.Score)
	}
}