Working with Maps in Go

Working with a Map in Go is like Dictionaries in Python, or Maps in Java. A Map stores information as key/value pairs. This is a nice thing about data structures, they are often found in other languages.

Defining the Map

When you define one in Go, you need to define the variable as a type called map, and then specify what the key and value will be. You don’t have to use a string and int, as is often seen in examples, it can be of any type that applies to your project, including your own user-defined data-type.

// general form
var data map[string]int

You can also use make if you want, or define it by giving it data.

// using make to define a map
myMap := make(map[string]int)

// defining a map by inference of the useage
myMap := map[string]int{
    "apple":  1,
    "banana": 2,
}

Adding and Updating Elements to the Map

To add elements to a map, you simply need to assign a value to a key that isn’t being used.

If you want to update an element, you will define a value to a key that is being used within the map.

// create elements in the map
myMap["apple"] = 1
myMap["banana"] = 2

// updating elements in the map
myMap["apple"] = 3

Removing Element From the Map

You can remove elements from a map using the delete() function.

delete(myMap, "banana")

Checking to see if a Key Exists

You can use a multi-result value to see if a key exists.

value, exists := myMap["grape"] 
if exists {
    // Key exists
} else {
    // Key does not exist
}

Iterating over the Map

You can loop over the values in a map using the for-each style of loop that Go provides.

for key, value := range myMap {
    fmt.Println(key, value)
}

Working with Maps in Go was originally found on Access 2 Learn