Go map data structure

Go comes with many data structures, including a map data structure.

A (hash)map maps keys to values, this is a common data structure in programming. Many languages support it including Go and Python (dictionary).

Unlike an array, it has a one to one mapping. The key can be used to quickly get the value without using a loop

m["Cat"] = "Meow"
fmt.Println(m["Cat"])

Above the key is "Cat" and the value is "Meow", which is then returned.

Introduction

You can use the make() function to create a map. If you call the make() function is returns a map initialized and ready for use.

In Go it's important to define the data types of the key and the value.
You can create all kind of maps, like a string to string mapping.

Example, map a key to a value where both are strings

var m map[string]string

// map key (string) to value (string)
m = make(map[string]string)

Go lets you map a key to value, where the value is an integer (int64):

var m map[string]int64

// map key (string) to value (integer)
m = make(map[string]int64)

Go Map Example

The example below creates a map (string -> string), sets a key pair and returns a value using a key. The map function makes the map. Then one (key,value) pair is set.

package main

import "fmt"

var m map[string]string

func main() {
    m = make(map[string]string)
    m["Cat"] = "Meow"
    fmt.Println(m["Cat"])
}

The output of the above program is

Meow

Program exited.

So the value was given for the key "Cat", the key pair is ("Cat","Meow").

An example of a key-value mapping with integers, where there are multiple items. The map function is used to initialize the map.

package main

import "fmt"

var m map[string]int64

func main() {
    m = make(map[string]int64)
    m["Serge"] = 33
    m["Thomas"] = 25
    m["Juan"] = 28
    fmt.Println(m["Serge"])
}

This program outputs:

33

Program exited.