A Golang map is a unordered collection of key-value pairs. For every key, there is a unique value. If you have a key, you can lookup the value in a map.

Sometimes its called an associative array or hash table. An example of a map in Go:

elements := make(map[string]string)

Its defines as a string to string mapping. In this example we’ll use the periodic elements.

You can map on other variable types too. Below an example of string to int mapping:

alpha := make(map[string]int)
alpha["A"] = 1

Map in golang

Map example

Create a new file named map.go, I like to use emacs, but any editor will do.

emacs -nw map.go

Copy the code below:

package main

import "fmt"

func main() {
    elements := make(map[string]string)
    elements["O"] = "Oxygen"
    elements["Ca"] = "Calcium"
    elements["C"] = "Carbon"

    fmt.Println(elements["C"])
    

Run your go program:

go run map.go

Hashmap

The above creation of code works but it’s a bit over expressive. You can define a map as a block of data, in which there is the same key value mapping.

alpha := map[string]int{
    "A" : 1,
    "B" : 2,
    "C" : 3,
}

This will do the exactly the same, but is a more elegant notation.

Store information

You can use a map to store information. We change the map, into a map of strings to maps of strings to strings.

website := map[string]map[string]string {

Then you can store information like this:

    website := map[string]map[string]string {
        "Google": map[string]string {
            "name":"Google",
            "type":"Search",
        },
        "YouTube": map[string]string {
            "name":"YouTube",
            "type":"video",
        },
    }

Then get a value using two keys,

fmt.Println(website["Google"]["name"])
fmt.Println(website["Google"]["type"])

Exercises

• What is a map?
• Is a map ordered?
• What can you use a map for?