英文:
Golang map put if absent?
问题
我有一个格式为 map[string]map[string]int 的地图。
在这个主地图中，我想要做类似于 Java 中的 putIfAbsent("key", new HashMap<>() 的操作。在 Go 语言中，有没有一种简洁的方式来实现这个功能呢？
英文:
I have a map of the format:
map[string]map[string]int
In this main map, I want to do something like putIfAbsent("key", new HashMap<>() as we have in Java. What is a clean and shorthand way to do it in Go?
答案1
得分: 7
你可以这样做：
var val map[string]intval, exists := m[key]if !exists {val = make(map[string]int)m[key] = val}
如果你在下面的代码中不需要 val：
if _, exists := m[key]; !exists {m[key] = make(map[string]int)}
英文:
You can do:
var val map[string]intval, exists := m[key]if !exists {val = make(map[string]int)m[key] = val}
If you don't need the val in the code coming below this:
if _,exists := m[key]; !exists {m[key]=make(map[string]int)}
答案2
得分: 2
如果您不打算立即使用该值，这里是代码的翻译部分：
m := make(map[string]map[string]int)if _, ok := m["unknown"]; !ok {m["unknown"] = make(map[string]int)}
以下是改进建议：
为了保持代码整洁和易于理解，您可以定义自己的类型。例如，如果您的数据是一个映射，表示“城市到人到年龄”，我会这样做：
type Person map[string]inttype City map[string]Personm := make(City)if _, ok := m["Dhaka"]; !ok {m["Dhaka"] = make(Person)}
英文:
If you don't intend to use the value right away, here you go...
m := make(map[string]map[string]int)if _, ok := m["unknown"]; !ok {m["unknown"] = make(map[string]int)}
Below is a suggestion for improvement:
To keep things clean and easy to understand, you can define your own types. For example, if your data is a mapping of "cities to persons to age", I would do it like this:
type Person map[string]inttype City map[string]Personm := make(City)if _, ok := m["Dhaka"]; !ok {m["Dhaka"] = make(Person)}
答案3
得分: 0
func main() {var testMap map[int]interface{}testMap = make(map[int]interface{})var addMap map[int]stringaddMap = make(map[int]string)addMap[1] = "999"addMap[2] = "888"Add(testMap, 111, addMap)for key, val := range testMap {fmt.Println(key)for key2, val2 := range val.(map[int]string) {fmt.Println(key2, val2)}}}func Add(_testMap map[int]interface{}, _key int, _val map[int]string) {_, exist := _testMap[_key]if exist == false {_testMap[_key] = _val} else {// do whatever you want}}
func main() {var testMap map[int]interface{}testMap = make(map[int]interface{})var addMap map[int]stringaddMap = make(map[int]string)addMap[1] = "999"addMap[2] = "888"Add(testMap, 111, addMap)for key, val := range testMap {fmt.Println(key)for key2, val2 := range val.(map[int]string) {fmt.Println(key2, val2)}}}func Add(_testMap map[int]interface{}, _key int, _val map[int]string) {_, exist := _testMap[_key]if exist == false {_testMap[_key] = _val} else {// do whatever you want}}
英文:
func main() {var testMap map[int]interface{}testMap = make(map[int]interface{})var addMap map[int]stringaddMap = make(map[int]string)addMap[1] = "999"addMap[2] = "888"Add(testMap, 111, addMap)for key, val := range testMap {fmt.Println(key)for key2, val2 := range val.(map[int]string) {fmt.Println(key2, val2)}}}
func Add(_testMap map[int]interface{}, _key int, _val map[int]string) {_, exist := _testMap[_key] // _ -> valueif exist == false {//addmap_testMap[_key] = _val} else {//whatever wanna to do}}
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