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Important Go Topics

Sorting in Go: sort and slices

Sort numbers, strings and structs, and write your own order with a comparison function.

  • Intermediate
  • 4 min read
  • 1 runnable example
What you'll learn
  • sort.Ints
  • slices.SortFunc
  • sort.Slice for structs
Run code →
Ranking
Leo95
Mia82
Zoe82
Ben67
Mia comes before Zoe because the scores are equal.

You decide the order

Go sorts slices in place. sort.Ints and sort.Strings cover the simple cases, and sort.Slice or slices.SortFunc take a function that decides the order.

slices.SortFunc compares two items and returns a negative number, zero or a positive number; comparing the lower-case forms ignores capital letters. sort.Slice takes a function that says whether item i comes before item j: here a higher score first, then the name.

Key points

  1. Sorting changes the slice in place.
  2. sort.Slice takes a less function.
  3. Break ties with a second comparison.

Runnable Go example

Go
Run code →
main.go
package main

import (
	"fmt"
	"slices"
	"sort"
	"strings"
)

type Student struct {
	Name  string
	Score int
}

func main() {
	numbers := []int{5, 2, 8, 1}
	sort.Ints(numbers)
	fmt.Println(numbers)

	words := []string{"pear", "Apple", "fig"}
	slices.SortFunc(words, func(a, b string) int {
		return strings.Compare(strings.ToLower(a), strings.ToLower(b))
	})
	fmt.Println(words)

	students := []Student{{"Mia", 82}, {"Leo", 95}, {"Zoe", 82}, {"Ben", 67}}
	sort.Slice(students, func(i, j int) bool {
		if students[i].Score != students[j].Score {
			return students[i].Score > students[j].Score
		}
		return students[i].Name < students[j].Name
	})
	for rank, student := range students {
		fmt.Printf("%d. %s (%d)\n", rank+1, student.Name, student.Score)
	}
}
Get a Run button for this example Result of running the code
[1 2 5 8]
[Apple fig pear]
1. Leo (95)
2. Mia (82)
3. Zoe (82)
4. Ben (67)

Practice

Open the example in the online compiler, change a value or add a line, and predict the output before you run it. Then break the code on purpose and read the compiler's message.

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