Golang map put if absent? - go

Question

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?

Answer 1

You can do:
var val map[string]int
val, 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)
}

Answer 2

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]int
type City map[string]Person
m := make(City)
if _, ok := m["Dhaka"]; !ok {
m["Dhaka"] = make(Person)
}

Answer 3

func main() {
var testMap map[int]interface{}
testMap = make(map[int]interface{})
var addMap map[int]string
addMap = 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] // _ -> value
if exist == false {
//addmap
_testMap[_key] = _val
} else {
//whatever wanna to do
}
}