How to modify golang map

Modification method: 1. Use the "map["key"]=value" statement to add or update elements. If "key" exists, update the element. If "key" does not exist, add the element. ; 2. Use the delete() function to delete the specified key-value pair from the map, the syntax is "delete(map, key name)"; 3. Re-create a new map object, which can clear all elements in the map, the syntax is "var mapname map[keytype]valuetype".

The operating environment of this tutorial: Windows 7 system, GO version 1.18, Dell G3 computer.

Map in Go language is a special data structure, an unordered collection of element pairs (pair). Pair corresponds to a key (index) and a value (value), so this structure is also called Associative array or dictionary is an ideal structure that can quickly find values. Given a key, the corresponding value can be quickly found.

map This data structure is also called dictionary (Python), hash, HashTable, etc. in other programming languages.

Introduction of map

[1] Map, a type built into the Go language, which relates key-value pairs Connection, we can get the corresponding value value through the key key. Similar to collections in other languages

[2]Basic syntax

var map变量名 map[keytype]valuetype

PS: Key and value types: bool, number, string, pointer, channel, and can also be Contains only the interfaces, structures, and arrays of the previous types
PS: key is usually int, string type, value is usually number (integer, floating point number), string, map, structure
PS: key: Slice, map, and function are not allowed

[3] Code:

Characteristics of map:

(1) Make
must be made before using the map collection (2) ) The key-value of the map is unordered
(3) The key cannot be repeated. If repeated, the latter value will replace the previous value
(4) The value can be repeated

package main
import "fmt"
func main(){
        //定义map变量：
        var a map[int]string
        //只声明map内存是没有分配空间
        //必须通过make函数进行初始化，才会分配空间：
        a = make(map[int]string,10) //map可以存放10个键值对
        //将键值对存入map中：
        a[20095452] = "张三"
        a[20095387] = "李四"
        a[20097291] = "王五"
        a[20095387] = "朱六"
        a[20096699] = "张三"
        //输出集合
        fmt.Println(a)
}

Three ways to create a map

 package main
import "fmt"
func main(){
        //方式1：
        //定义map变量：
        var a map[int]string
        //只声明map内存是没有分配空间
        //必须通过make函数进行初始化，才会分配空间：
        a = make(map[int]string,10) //map可以存放10个键值对
        //将键值对存入map中：
        a[20095452] = "张三"
        a[20095387] = "李四"
        //输出集合
        fmt.Println(a)
        //方式2：
        b := make(map[int]string)
        b[20095452] = "张三"
        b[20095387] = "李四"
        fmt.Println(b)
        //方式3：
        c := map[int]string{
                20095452 : "张三",
                20098765 : "李四",
        }
        c[20095387] = "王五"
        fmt.Println(c)
}

##Add, delete, modify and check the map

【1】Add and update operations:

map["key"]= value ——》If the key does not exist, it is added, if the key exists, it is modified.

[2] Delete operation:

delete(map, "key") , delete is a built-in function. If the key exists, delete the key-value. If y of k does not exist, no operation will be performed, but no error will be reported

[3] Clear operation:

(1) If we want to delete the map There is no special method to delete all the keys at once. You can traverse the keys and delete them one by one

(2) or

map = make(...), make a new one, and make the original one Become garbage and be recycled by gc

[4] Search operation:

value, bool = map[key]

value is the returned value, bool is whether to return, or true or false

package main
import "fmt"
func main(){
        //定义map
        b := make(map[int]string)
        //增加：
        b[20095452] = "张三"
        b[20095387] = "李四"
        //修改：
        b[20095452] = "王五"
        //删除：
        delete(b,20095387)
        delete(b,20089546)
        fmt.Println(b)
        //查找：
        value,flag := b[200]
        fmt.Println(value)
        fmt.Println(flag)
}

[5] Get the length: len function

[6] Traverse: for-range

package main
import "fmt"
func main(){
        //定义map
        b := make(map[int]string)
        //增加：
        b[20095452] = "张三"
        b[20095387] = "李四"
        b[20098833] = "王五"
        //获取长度：
        fmt.Println(len(b))
        //遍历：
        for k,v := range b {
                fmt.Printf("key为：%v value为%v \t",k,v)
        }
        fmt.Println("---------------------------")
        //加深难度：
        a := make(map[string]map[int]string)
        //赋值：
        a["班级1"] = make(map[int]string,3)
        a["班级1"][20096677] = "露露"
        a["班级1"][20098833] = "丽丽"
        a["班级1"][20097722] = "菲菲"
        a["班级2"] = make(map[int]string,3)
        a["班级2"][20089911] = "小明"
        a["班级2"][20085533] = "小龙"
        a["班级2"][20087244] = "小飞"
        for k1,v1:= range a {
                fmt.Println(k1)
                for k2,v2:= range v1{
                        fmt.Printf("学生学号为：%v 学生姓名为%v \t",k2,v2)
                }
                fmt.Println()
        }
}

[Related recommendations:

Go video tutorial、Programming teaching】

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