Map

Sriparno08's avatar
Sriparno08's avatar
Sriparno08
Published Dec 22, 2022Updated May 13, 2025
Contribute to Docs

In Go, a map is a built-in data structure that is used to store a collection of unordered key-value pairs. The pairs can be of the same data type or mixed types. It is Go’s implementation of a hash table, which allows for efficient access, insertion, and deletion.

Creating a Map

An empty map can be created using the make() function:

variable_name := make(map[key_data_type]value_data_type)

An empty map can also be created using a map literal:

variable_name := map[key_data_type]value_data_type{}

A map literal can also be used for initializing a map:

map_name := map[key_data_type]value_data_type{
  key-1: value-1,
  key-2: value-2,
  key-N: value-N,
}

Example

This example shows how to create a map using these methods:

package main
import "fmt"


func main() {
  // Create a map using make()
  gradebook1 := make(map[string]float32)


  // Create a map using a map literal
  gradebook2 := map[string]float32{}


  // Initialize a map using a map literal
  gradebook3 := map[string]float32{"John": 85.2, "Ana": 95.6}


  // Print the maps
  fmt.Println(gradebook1)
  fmt.Println(gradebook2)
  fmt.Println(gradebook3)
}

This will return the following output:

map[]
map[]
map[Ana:95.6 John:85.2]

Note: All pairs should terminate with a comma, including the final pair, unless the assignment is all made on one line.

Accessing Items in a Map

A value in a map can be accessed by putting its corresponding key in brackets after the map name:

map_name[key_value]

If the key does not exist, the zero value will be returned based on the data type of the values in the map (e.g. int: 0, bool: false).

Example

Here is an example that prints the corresponding value for the key "John":

package main
import "fmt"


func main() {
  // Initialize a map
  gradebook := map[string]float32{"John": 85.2, "Ana": 95.6}


  // Print the value for the key "John"
  fmt.Println(gradebook["John"])
}

This will return the following output:

85.2

Adding Items to a Map

New key-value pairs can be added to a map by setting a new key to a new value:

map_name[new_key] = [new_value]

Example

This example adds two new key-value pairs to a map:

package main
import "fmt"


func main() {
  // Initialize a map
  gradebook := map[string]float32{"John": 85.2, "Ana": 95.6}


  // Add two new key-value pairs to the map
  gradebook["George"] = 76.4
  gradebook["Emma"] = 90


  // Print the map
  fmt.Println(gradebook)
}

This will output:

map[Ana:95.6 Emma:90 George:76.4 John:85.2]

Removing Items from a Map

Key-value pairs can be removed from a map with the built-in delete() function:

delete(map_name, existing_key)

Example

This example removes a key-value pair from a map:

package main
import "fmt"


func main() {
  // Initialize a map
  gradebook := map[string]float32{"John": 85.2, "Ana": 95.6}


  // Delete an item from the map
  delete(gradebook, "John")


  // Print the map
  fmt.Println(gradebook)
}

This will output:

map[Ana:95.6]

Iterating Over a Map

This example uses the for...range loop to iterate over a map:

package main
import "fmt"


func main() {
  // Initialize a map
  gradebook := map[string]float32{"John": 85.2, "Ana": 95.6}


  /// Iterate over the map and print its items
  for key, value := range gradebook {
    fmt.Printf("(%s, %.1f)\n", key, value)
  }
}

This will output:

(John, 85.2)
(Ana, 95.6)

Frequently Asked Questions

1. Can a map key be any type in Go?

No. In Go, map keys must be comparable types, such as strings, integers, or structs that do not contain slices, maps, or functions.

2. Are Go maps ordered?

No. Maps in Go are unordered, and their iteration order is not guaranteed to be the same every time.

3. Are maps thread-safe in Go?

No. Maps are not safe for concurrent use. Use sync.Map or synchronization techniques if needed.

All contributors

Contribute to Docs

Learn Go on Codecademy