map/字典

key-value的數據結構，又叫字典或關聯數組（map是無序的）

聲明：

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

聲明是不會分配內存的，初始化需要make

創建方式：

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)
}

輸出：
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相關操作：

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 {//遍歷
fmt.Println(k,v)
}
delete(a, “hello”)//刪除
len(a)//長度

查找/修改的用法舉例：

func modify(a map[string]map[string]string) {
    _, ok := a["zhangsan"]
    if !ok {
        //要記得初始化(是map類型的)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()
}

遍歷值為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))
}

輸出：
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是引用類型

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. 先獲取所有key，把key進行排序
b. 按照排序好的key，進行遍歷

map反轉：

a. 初始化另外一個map，把key、value互換即可

map的值也可以是map：

a := make(map[string]map[string]string, 10)
    /*//報錯！作為值的map[string]string也要初始化才行
    a["k1"]["k2"] = "哈哈"
    fmt.Println(a)*/
    //作為值的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)