Basic Tutorials of Redis - List

Posted 2020-08-08 Catcher Wong

Basic Tutorials of Redis(6) - List

　　Redis\'s List is different from C#\'s List,but similar with C#\'s LinkedList.Sometimes I confuse with them.I expect

that you won\'t mix them and have a clear mind of them.

　　There are 17 commands we can use in List.

　　

 　　Push and pop are the base opreation of the linkediist,either as Redis\'s List.When we want to store the

list, lpush and rpush can help us to save the data.Both of them can save one or more values to the key.Now

I add element 11 to the key named list-1,then add element 12 and 13 to this key.Here\'re the commands and result.

lpush list-1 11
lpush list-1 12 13

 　　The code demonstrated above push the element from left to the right.As all we know,linkedlist has anonther

way to push the elements.rpush is the another way.For example,I push the same elements to the key named list-2.

Taking the following code and result.

rpush list-2 11
rpush list-2 12 13

 　　By using those two commands to store the data,we don\'t know the Difference between them apparently.But when

you select all of the elements,you will find out something.Using lrange can make us know the elements in the list.

lrange list-1 0 -1

lrange list-2 0 -1 

 　　The next picture explain the result clearly.You can combine the linkedlist\'s feature to think about the result.

　　We also can insert an element before or after another element.Redis provides a command for us.For an instance,

I insert 90 before 12 on list-1 ,and insert 80 after 12.You will get the following result.

linsert list-1 before 12 90
linsert list-1 after 12 80

 　　Sometimes we may want to know how many elements in the list?Just as the length of a string.We use llen to

get the length of the list.

llen list-1 

　　We also can get the elements by their own index in the list.

lindex list-1 2

　　We also can modify the elements by their index.

lset list-1 2 66

　　The next time I will show you how to remove the elements from the list.There are three commands can help

us to remove elements.

　　lpop will remove the leftmost element from the list.And the client will return the removed element.

lpop list-1

 　　rpop will remove the rightmost element from the list.And the client will return the removed element as well.

rpop list-1

 　　lrem will remove the count occurrences of elements equal to value.If count > 0,it will remove elements moving

from head to tail.If count < 0,it will remove elements moving from tail to head.If count = 0,it will remove all elements

equal to value.

lrem list-1 2 66

 

　　The following code demonastrates the basic usage of List in StackExchange.Redis.

 1              //lpush
 2             db.ListLeftPush("list-1", 11);
 3             var list_1 = new RedisValue[2] { 12,13};
 4             db.ListLeftPush("list-1", list_1);
 5             Console.WriteLine("after lpush:");
 6             foreach (var item in db.ListRange("list-1"))
 7             {
 8                 Console.Write(item+" ");
 9             }
10             Console.WriteLine("");
11             //rpush
12             db.ListRightPush("list-2", 11);
13             var list_2 = new RedisValue[2] { 12, 13 };
14             db.ListRightPush("list-2", list_1);
15             Console.WriteLine("after rpush:");
16             foreach (var item in db.ListRange("list-2"))
17             {
18                 Console.Write(item + " ");
19             }
20             Console.WriteLine("");
21             //linsert
22             db.ListInsertBefore("list-1",12,90);
23             Console.WriteLine("after linsert 90 before 12:");
24             foreach (var item in db.ListRange("list-1"))
25             {
26                 Console.Write(item + " ");
27             }
28             db.ListInsertAfter("list-1", 12, 80);
29             Console.WriteLine("\\nafter linsert 80 after 12:");
30             foreach (var item in db.ListRange("list-1"))
31             {
32                 Console.Write(item + " ");
33             }
34             Console.WriteLine("");
35             //llen
36             Console.WriteLine(string.Format("the length of list-1 is {0}",db.ListLength("list-1")));
37             //lindex
38             Console.WriteLine(string.Format("the element in the second index is {0}", db.ListGetByIndex("list-1",2)));
39             //lset
40             db.ListSetByIndex("list-1", 2, 66);
41             Console.WriteLine("after lset 66 from index 2:");
42             foreach (var item in db.ListRange("list-1"))
43             {
44                 Console.Write(item + " ");
45             }
46             Console.WriteLine("");
47             //lpop
48             Console.WriteLine(string.Format("lpop element {0}", db.ListLeftPop("list-1")) );
49             //rpop
50             Console.WriteLine(string.Format("rpop element {0}", db.ListRightPop("list-1")));
51             //lrem
52             db.ListRemove("list-1", 66,2);
53             Console.WriteLine("after remove:");
54             foreach (var item in db.ListRange("list-1"))
55             {
56                 Console.Write(item + " ");
57             }

　　When you debug the codes,the results are as follow.

　　

　　The next post of this series is the basic opreation of publish and subscribe in Redis.Thanks for your reading