SRANDMEMBER

SRANDMEMBER

1. 不指定count时，默认随机返回一个成员
2. 指定count时，如果count小于集合成员数，则返回一个包含count个随机元素的List。
3. 指定count时，如果count大于等于集合成员数，则以List形式返回整个集合
4. 如果count为负数，且count的绝对值小于集合成员数，则返回一个包含count个随机元素的List，但是元素可能会重复出现多次
5. 如果count为负数，且count的绝对值等于或者大于集合成员数，则返回一个包含count个随即元素的List，元素同样可能会重复多次。但是，即使count绝对值大于集合成员数，但是也不一定会返回所有集合成员
6. 如果指定count为0，则返回一个空列表

Command

$ redis-cli.exe -h 127.0.0.1 -p 6379
127.0.0.1:6379> sadd boa 1 2 3 4
(integer) 4
127.0.0.1:6379> srandmember boa
"4"
127.0.0.1:6379> srandmember boa 2
1) "3"
2) "1"
127.0.0.1:6379> srandmember boa 5
1) "1"
2) "2"
3) "3"
4) "4"
127.0.0.1:6379> srandmember boa -3
1) "3"
2) "3"
3) "4"
127.0.0.1:6379> srandmember boa -4
1) "3"
2) "2"
3) "1"
4) "3"
127.0.0.1:6379> srandmember boa -5
1) "1"
2) "3"
3) "4"
4) "4"
5) "1"
127.0.0.1:6379> srandmember boa 0
(empty list or set)

Code

func srandmember(c redis.Conn) {
    defer c.Do("DEL", "boa")
    c.Do("SADD", "boa", 1, 2, 3, 4)
    //  1. If you don't specify count, will return a rand member as default.
    randMember, err := redis.Int(c.Do("SRANDMEMBER", "boa"))
    if err != nil {
        colorlog.Error(err.Error())
        return
    }
    fmt.Println("If you don't specify a number, will return a rand member as default:", randMember)
    //  2. If specified count is less than the number of members of set,
    //  will return a list containing count random members.
    randMembers, err := redis.Ints(c.Do("SRANDMEMBER", "boa", 2))
    if err != nil {
        colorlog.Error(err.Error())
        return
    }
    fmt.Println("If specified count is less than the number of members of set,")
    fmt.Println("will return a list containing count random members:", randMembers)
    //  3. If specified count is greater than or equal with the number of members of set,
    //  will return a list containing all the members.
    randMembers, err = redis.Ints(c.Do("SRANDMEMBER", "boa", 5))
    if err != nil {
        colorlog.Error(err.Error())
        return
    }
    fmt.Println("If specified count is greater than or equal with the number of members of set,")
    fmt.Println("will return a list containing all the members:", randMembers)
    //  4. If specified count is a negative number and count's absolute value is less than the number of members of set
    //  will return a list containing count random members.
    //  But some elements may be repeated many times.
    randMembers, err = redis.Ints(c.Do("SRANDMEMBER", "boa", -3))
    if err != nil {
        colorlog.Error(err.Error())
        return
    }
    fmt.Println("If specified count is a negative number, " +
        "and count's absolute value is less than the number of members of set")
    fmt.Println("will return a list containing count random members.")
    fmt.Println("But some elements may be repeated many times:", randMembers)
    //  5. If specified count is a negative number and count's absolute value is greater than or equal with
    //  the number of members of set, will return a list containing count random members.
    //  But some elements may be repeated many times.
    randMembers, err = redis.Ints(c.Do("SRANDMEMBER", "boa", -4))
    if err != nil {
        colorlog.Error(err.Error())
        return
    }
    fmt.Println("If specified count is a negative number " +
        "and count's absolute value is greater than or equal with the number of members of set,")
    fmt.Println("will return a list containing count random members.")
    fmt.Println("But some elements may be repeated many times:", randMembers)
    randMembers, err = redis.Ints(c.Do("SRANDMEMBER", "boa", -5))
    if err != nil {
        colorlog.Error(err.Error())
        return
    }
    fmt.Println("But some elements may be repeated many times:", randMembers)
    //  6. If count is 0, will return an empty list.
    nilRandMember, err := redis.Ints(c.Do("SRANDMEMBER", "boa", 0))
    if err != nil {
        colorlog.Error(err.Error())
        return
    }
    if len(nilRandMember) == 0 {
        fmt.Println("If count is 0, will return an empty list.")
    }
}

Output

$ go run main.go 
If you don't specify a number, will return a rand member as default: 4
If specified count is less than the number of members of set,
will return a list containing count random members: [3 1]
If specified count is greater than or equal with the number of members of set,
will return a list containing all the members: [1 2 3 4]
If specified count is a negative number, and count's absolute value is less than the number of members of set
will return a list containing count random members.
But some elements may be repeated many times: [1 3 3]
If specified count is a negative number and count's absolute value is greater than or equal with the number of members of set,
will return a list containing count random members.But some elements may be repeated many times: [4 4 1 3]
But some elements may be repeated many times: [3 1 3 3 1]
If count is 0, will return an empty list.