Lesson 3
Working with Maps and Sorting in Go
Working with Maps and Sorting in Go

This lesson's topic is working with Maps and Sorting in Go. Learning to access map data in order enriches our toolkit for organized and efficient data manipulation.

Using Maps and the sort Package

Go's sort package helps us access map data in a sorted fashion. To illustrate, we create a map and use slices to sort keys, allowing us to display map values in order.

One approach we can take is to extract all keys int a slice, sort this slice, and print the values in a natural order (alphabetically). Here's an example:

Go
1package main
2
3import (
4    "fmt"
5    "sort"
6)
7
8func main() {
9    // Map with fruits as keys and corresponding counts as values
10    fruitCounts := map[string]int{
11        "banana": 3,
12        "apple":  4,
13        "pear":   1,
14        "orange": 2,
15    }
16
17    // Extract and sort keys
18    keys := make([]string, 0, len(fruitCounts))
19    for key := range fruitCounts {
20        keys = append(keys, key)
21    }
22    sort.Strings(keys)
23
24    // Print fruits in sorted order by keys
25    for _, key := range keys {
26        fmt.Printf("%s=%d\n", key, fruitCounts[key])
27    }
28}

The output will be:

1apple=4
2banana=3
3orange=2
4pear=1
Operations with Sorted Access

Using slices to sort keys, we can implement functionalities for map operations like existence checks and removals, accessing elements in a sorted order:

Go
1package main
2
3import (
4    "fmt"
5    "sort"
6)
7
8func main() {
9    // Initialize the map
10    fruitCounts := map[string]int{
11        "banana": 3,
12        "apple":  4,
13        "pear":   1,
14        "orange": 2,
15    }
16
17    // Check existence
18    if _, exists := fruitCounts["apple"]; exists {
19        fmt.Println("Contains 'apple' key: True")
20    }
21
22    // Remove an element
23    delete(fruitCounts, "apple")
24    if _, exists := fruitCounts["apple"]; !exists {
25        fmt.Println("Removed 'apple': True") // Output: True
26    }
27
28    // Fetch non-existent key
29    value, exists := fruitCounts["apple"]
30    if !exists {
31        fmt.Println("Value: Not found") // Output: Value: Not found
32    } else {
33        fmt.Printf("Value: %d\n", value)
34    }
35
36    // Find and display the last element in sorted key order
37    keys := make([]string, 0, len(fruitCounts))
38    for key := range fruitCounts {
39        keys = append(keys, key)
40    }
41    sort.Strings(keys)
42    lastKey := keys[len(keys)-1]
43    fmt.Printf("Last entry: %s=%d\n", lastKey, fruitCounts[lastKey]) // Output: pear=1
44}
Lesson Summary

You've explored how to sort access in Go using regular maps. This included extracting and sorting keys with the sort package to access map values in order, and performing essential operations. Continue practicing to deepen your understanding of maps and sorting in Go.

Enjoy this lesson? Now it's time to practice with Cosmo!
Practice is how you turn knowledge into actual skills.