Go – For Loop Map

Maps in Go are key-value pairs, and the for loop with the range keyword is commonly used to traverse them.

In this tutorial, we will provide practical examples along with detailed explanations to demonstrate how to iterate over maps using For Loop.

Iterating Over Maps Using For Loop

The range keyword allows you to iterate over maps in Go. It returns two values during each iteration: the key and the value.

Example 1: Iterating Over a Map

In this example, we will iterate over a map and print both its keys and values:

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package main

import "fmt"

func main() {
    // Declare a map
    countries := map[string]string{
        "US": "United States",
        "IN": "India",
        "JP": "Japan",
    }

    // Iterate over the map
    for key, value := range countries {
        fmt.Printf("Key: %s, Value: %s\n", key, value)
    }
}

Explanation

  1. Declare a Map: A map named countries is initialized with key-value pairs where keys are country codes, and values are country names.
  2. Use Range: The range keyword iterates over the map, returning each key and its corresponding value.
  3. Print Key-Value Pairs: The key and value are printed using fmt.Printf.

Output

Example 2: Iterating Over Keys Only

If you only need the keys of a map, you can ignore the value by using the underscore (_):

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package main

import "fmt"

func main() {
    // Declare a map
    countries := map[string]string{
        "US": "United States",
        "IN": "India",
        "JP": "Japan",
    }

    // Iterate over the map keys
    for key := range countries {
        fmt.Println("Key:", key)
    }
}

Explanation

  1. Declare a Map: The map countries is initialized with key-value pairs.
  2. Use Range: The range keyword is used to iterate over the map keys.
  3. Ignore Values: By omitting the value and using only the key, the loop focuses on printing the keys.

Output

Example 3: Iterating Over Values Only

If you only need the values of a map, you can ignore the keys:

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package main

import "fmt"

func main() {
    // Declare a map
    countries := map[string]string{
        "US": "United States",
        "IN": "India",
        "JP": "Japan",
    }

    // Iterate over the map values
    for _, value := range countries {
        fmt.Println("Value:", value)
    }
}

Explanation

  1. Declare a Map: The map countries is initialized with key-value pairs.
  2. Use Range: The range keyword iterates over the map, returning only the values.
  3. Ignore Keys: The underscore (_) is used to ignore the keys while focusing on the values.

Output

When to Use For Loop with Maps

You can use For Loop with Maps:

  • To process or manipulate both keys and values.
  • To retrieve all keys or values for specific operations.
  • To filter or search for specific elements in the map.

Conclusion

The for loop with range provides a simple and efficient way to iterate over maps in Go. By selectively using keys or values, you can handle map data effectively to suit your program’s requirements. Understanding these patterns will help you process and manipulate maps efficiently.