Polar Snow Documentation

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Go基础之Map

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map中的key

Go语言中对map中的key的数据类型有如下要求:

  • map使用哈希表, key必须可以比较相等
  • 除了slice, map, function的内建类型都可以作为key
  • struct类型如果不包含第二条中排除的数据类型, 也可以做为key

map的声明与赋值

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package main

import "fmt"

func main() {
	m := map[string]string {
		"name": "larry",
		"company": "PolarSnow Inc.",
		"website": "https://lvrui.io",
	}
	fmt.Println(m)
}

执行结果:

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map[name:larry company:PolarSnow Inc. website:https://lvrui.io]

嵌套Map

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package main

import "fmt"

func main() {
	m := map[string]map[string]string {
		"member": {
			"name": "larry",
			"company": "PolarSnow Inc.",
			"website": "https://lvrui.io",
		},
	}
	fmt.Println(m["member"]["name"])
}

执行结果:

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larry

其他声明map的方式

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package main

import "fmt"

func main() {
	m := make(map[string]string)  // m == empty map
	var mm map[string]string  // mm == nil
	fmt.Println(m, mm)
}

执行结果:

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map[] map[]

map的遍历

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package main

import "fmt"

func main() {
	m := map[string]string {
		"name": "larry",
		"company": "PolarSnow Inc.",
		"website": "https://lvrui.io",
	}

	for k, v := range m {
		fmt.Println(k, v)
	}
}

执行结果:

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company PolarSnow Inc.
website https://lvrui.io
name larry

注意: map是无序的

读取map中的值

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package main

import "fmt"

func main() {
	m := map[string]string {
		"name": "larry",
		"company": "PolarSnow Inc.",
		"website": "https://lvrui.io",
	}

	fmt.Println(m["website"])

	fmt.Println(m["site"])  // map中无此key, 但是不会报错, 拿到的是string的zero value

	// 通常判断map取值有没有成功的方式
	if address, ok := m["website"]; ok {
		fmt.Println(address)
	} else {
		fmt.Println("Key does not exist")
	}
	
}

执行结果:

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https://lvrui.io

https://lvrui.io

增加/修改元素

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package main

import "fmt"

func main() {
	m := map[string]string {
		"name": "larry",
		"company": "PolarSnow Inc.",
		"website": "https://lvrui.io",
	}

	fmt.Println(m)

	m["country"] = "China"

	fmt.Println(m)

	m["name"] = "Polar Snow"

	fmt.Println(m)

}

执行结果:

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map[company:PolarSnow Inc. website:https://lvrui.io name:larry]
map[name:larry company:PolarSnow Inc. website:https://lvrui.io country:China]
map[name:Polar Snow company:PolarSnow Inc. website:https://lvrui.io country:China]

Go对map添加/修改元素的操作形式, 与Python相同

删除元素

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package main

import "fmt"

func main() {
	m := map[string]string {
		"name": "larry",
		"company": "PolarSnow Inc.",
		"website": "https://lvrui.io",
	}

	fmt.Println(m)

	delete(m, "company")

	fmt.Println(m)

}

执行结果:

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map[name:larry company:PolarSnow Inc. website:https://lvrui.io]
map[name:larry website:https://lvrui.io]

获取map元素的个数

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package main

import "fmt"

func main() {
	m := map[string]string {
		"name": "larry",
		"company": "PolarSnow Inc.",
		"website": "https://lvrui.io",
	}

	fmt.Println(len(m))
}

执行结果:

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3

map的应用

取出所有key和所有value

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package main

import "fmt"

func main() {
	m := map[string]string {
		"name": "larry",
		"company": "PolarSnow Inc.",
		"website": "https://lvrui.io",
	}

	var key []string
	var value []string

	for k, v := range m {
		key = append(key, k)
		value = append(value, v)
	}

	fmt.Println(key)
	fmt.Println(value)

}

执行结果:

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[name company website]
[larry PolarSnow Inc. https://lvrui.io]
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