map/字典

key-value的数据结构，又叫字典或关联数组（map是无序的）

---

声明：

var map1 map[keytype]valuetype
var a map[string]string
var a map[string]int
var a map[int]string
var a map[string]map[string]string

声明是不会分配内存的，初始化需要make

创建方式：

package main

import "fmt"

func main() {
	a := make(map[string]string, 10)
	fmt.Println(a)
	a["a"] = "aa"
	a["b"] = "bb"
	fmt.Println(a)
	var b map[string]string = map[string]string {
		"b1": "v1",
		"b2": "v2",
	}
	fmt.Println(b)
	var c = map[string]string {
		"c1": "v1",
		"c2": "v2",
	}
	fmt.Println(c)
	d := map[string]string {
		"d1": "v1",
		"d2": "v2",
	}
	fmt.Println(d)
}

输出： map[] map[a:aa b:bb] map[b1:v1 b2:v2] map[c1:v1 c2:v2] map[d1:v1 d2:v2]

Process finished with exit code 0

---

map相关操作：

var a map[string]string = map[string]string{“hello”: “world”}
a = make(map[string]string, 10)
a[“hello”] = “world”//插入和更新
Val, ok := a[“hello”]//查找
for k, v := range a {//遍历
fmt.Println(k,v)
}
delete(a, “hello”)//删除
len(a)//长度

查找/修改的用法举例：

func modify(a map[string]map[string]string) {
	_, ok := a["zhangsan"]
	if !ok {
		//要记得初始化(是map类型的)值
		a["zhangsan"] = make(map[string]string)
	}
	a["zhangsan"]["passwd"] = "123456"
	a["zhangsan"]["nickname"] = "pangpang"
	return
}
func testMap3() {
	a := make(map[string]map[string]string, 100)
	modify(a)
	fmt.Println(a)
}
func main() {
	testMap3()
}

遍历值为map的map：

package main

import "fmt"

func trans(a map[string]map[string]string) {
	for k, v := range a {
		fmt.Println(k)
		for k1, v1 := range v {
			fmt.Println("\t", k1, v1)
		}
	}
}

func main() {
	a := make(map[string]map[string]string, 100)
	a["key1"] = make(map[string]string)
	a["key1"]["key2"] = "abc"
	a["key1"]["key3"] = "abc"
	a["key1"]["key4"] = "abc"
	a["key1"]["key5"] = "abc"

	a["key2"] = make(map[string]string)
	a["key2"]["key2"] = "abc"
	a["key2"]["key3"] = "abc"

	trans(a)
	delete(a, "key1")
	fmt.Println()
	trans(a)

	fmt.Println(len(a))
}

输出： key1 key2 abc key3 abc key4 abc key5 abc key2 key2 abc key3 abc

key2 key2 abc key3 abc 1

Process finished with exit code 0 map是引用类型

func modify(a map[string]int) {
a[“one”] = 134
}

slice of map：

Items := make([]map[int][int], 5)
For I := 0; I < 5; i++ {
        items[i] = make(map[int][int])
}

map排序：

a. 先获取所有key，把key进行排序
b. 按照排序好的key，进行遍历

map反转：

a. 初始化另外一个map，把key、value互换即可

---

map的值也可以是map：

a := make(map[string]map[string]string, 10)
	/*//报错！作为值的map[string]string也要初始化才行
	a["k1"]["k2"] = "哈哈"
	fmt.Println(a)*/
	//作为值的map[string]string也要初始化才行！
	a["k1"] = make(map[string]string)
	a["k1"]["k2"] = "哈哈"
	a["k1"]["k3"] = "呵呵"
	a["k1"]["k4"] = "嘿嘿"
	fmt.Println(a)