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This article introduces how to create a Map of Maps in Go language.

GoLang Map of Map

Maps of Maps or nested maps are those maps whose key-value pairs are also maps. In Go language, you can create Maps of Maps.

When we define a Map, we have to define the type of key and value. In this case, the type of key can be int, string or any other type and the type of value will again be map.

grammar:

var DemoMap = map[string]map[string]string{}
// 或者

var DemoMap = map[int]map[string]string{}

As you can see, DemoMap defines a key string, int type, and a value of map type. Let's take an example.

Code:

package main
import "fmt"

func main() {
    DemoMap := map[int]map[string]string{
        1: {
            "one":   "Jiyik1",
            "two":   "Jiyik2",
            "three": "Jiyik3",
        },
        2: {
            "four": "Jiyik4",
            "five": "Jiyik5",
            "Six":  "Jiyik6",
        },
        3: {
            "seven": "Jiyik7",
            "eight": "Jiyik8",
            "nine":  "Jiyik9",
        },
        4: {
            "ten":    "Jiyik10",
            "eleven": "Jiyik11",
            "twelve": "Jiyik12",
        },
    }
    fmt.Println(DemoMap)
}

The above code creates a Map containing key integers and value Map<int> and then prints the Map.

Output:

map[
    1:map[one:Jiyik1 three:Jiyik3 two:Jiyik2]
    2:map[Six:Jiyik6 five:Jiyik5 four:Jiyik4]
    3:map[eight:Jiyik8 nine:Jiyik9 seven:Jiyik7]
    4:map[eleven:Jiyik11 ten:Jiyik10 twelve:Jiyik12]]

Deleting a Nested Map

We can use GoLang's delete()method to delete a nested Map. It takes two parameters, one is the key parent mapand the other is the nested map key.

Let’s take an example.

Code:

package main
import "fmt"

func main() {
    DemoMap := map[int]map[string]string{
        1: {
            "one":   "Jiyik1",
            "two":   "Jiyik2",
            "three": "Jiyik3",
        },
        2: {
            "four": "Jiyik4",
            "five": "Jiyik5",
            "Six":  "Jiyik6",
        },
        3: {
            "seven": "Jiyik7",
            "eight": "Jiyik8",
            "nine":  "Jiyik9",
        },
        4: {
            "ten":    "Jiyik10",
            "eleven": "Jiyik11",
            "twelve": "Jiyik12",
        },
    }
    delete(DemoMap, 3)
    fmt.Println(DemoMap)
}

The above code will remove the nested Map at key 3 from the parent Map.

Output:

map[
    1:map[one:Jiyik1 three:Jiyik3 two:Jiyik2]
    2:map[Six:Jiyik6 five:Jiyik5 four:Jiyik4]
    4:map[eleven:Jiyik11 ten:Jiyik10 twelve:Jiyik12]]

Similarly, we can remove a member of a nested Map using the same delete()method where the first argument will be the nested Map and the second argument will be the key we want to remove.

Code:

package main
import "fmt"

func main() {
    DemoMap := map[int]map[string]string{
        1: {
            "one":   "Jiyik1",
            "two":   "Jiyik2",
            "three": "Jiyik3",
        },
        2: {
            "four": "Jiyik4",
            "five": "Jiyik5",
            "Six":  "Jiyik6",
        },
        3: {
            "seven": "Jiyik7",
            "eight": "Jiyik8",
            "nine":  "Jiyik9",
        },
        4: {
            "ten":    "Jiyik10",
            "eleven": "Jiyik11",
            "twelve": "Jiyik12",
        },
    }
    delete(DemoMap[3], "seven")
    fmt.Println(DemoMap)
}

The above code will delete the member with key 3 and member key 7 in the nested Map.

Output:

map[
    1:map[one:Jiyik1 three:Jiyik3 two:Jiyik2]
    2:map[Six:Jiyik6 five:Jiyik5 four:Jiyik4]
    3:map[eight:Jiyik8 nine:Jiyik9]
    4:map[eleven:Jiyik11 ten:Jiyik10 twelve:Jiyik12]]

Iterating over a nested Map

To iterate over a nested Map, we have to use for loop giving the index number of the Map. Let us take an example of iterating over a nested Map.

Code:

package main
import "fmt"

func main() {
    DemoMap := map[int]map[string]string{
        1: {
            "one":   "Jiyik1",
            "two":   "Jiyik2",
            "three": "Jiyik3",
        },
        2: {
            "four": "Jiyik4",
            "five": "Jiyik5",
            "Six":  "Jiyik6",
        },
        3: {
            "seven": "Jiyik7",
            "eight": "Jiyik8",
            "nine":  "Jiyik9",
        },
        4: {
            "ten":    "Jiyik10",
            "eleven": "Jiyik11",
            "twelve": "Jiyik12",
        },
    }
    for key, value := range DemoMap[3] {
        fmt.Println(key, value)
    }
}

The above code will iterate over the Map at the third position in the parent Map.

Output:

seven Jiyik7
eight Jiyik8
nine Jiyik9