Go Academy · Lesson

Sorting Slices

sort.Slice and helpers.

Sorting Slices is a free Go Academy lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Go Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Why Sorting Matters

Sorting puts elements in a defined order. Go's sort package from the standard library handles this efficiently.

You rarely write your own sort algorithm in Go. Instead you call helpers that work on slices.

Importing sort

To use the package, import it with import "sort". It lives in the standard library, so no external download is needed.

package main

import (
	"fmt"
	"sort"
)

func main() {
	fmt.Println("sort imported")
	_ = sort.IntsAreSorted([]int{1, 2, 3})
}

Sorting Integers

sort.Ints sorts a slice of int in ascending order, in place. The original slice is modified.

package main

import (
	"fmt"
	"sort"
)

func main() {
	nums := []int{5, 2, 8, 1, 9}
	sort.Ints(nums)
	fmt.Println(nums)
}

Sorting Strings

sort.Strings sorts a slice of strings lexicographically (alphabetical, byte order).

package main

import (
	"fmt"
	"sort"
)

func main() {
	words := []string{"banana", "apple", "cherry"}
	sort.Strings(words)
	fmt.Println(words)
}

Sorting Floats

sort.Float64s sorts a slice of float64 values in ascending order.

package main

import (
	"fmt"
	"sort"
)

func main() {
	values := []float64{3.2, 1.5, 2.8}
	sort.Float64s(values)
	fmt.Println(values)
}

sort.Slice

sort.Slice sorts any slice using a less function you supply. The function takes two indices i and j and returns true if element i should come before j.

package main

import (
	"fmt"
	"sort"
)

func main() {
	nums := []int{5, 2, 8, 1}
	sort.Slice(nums, func(i, j int) bool {
		return nums[i] < nums[j]
	})
	fmt.Println(nums)
}

Descending Order

To sort descending, flip the comparison in the less function: return nums[i] > nums[j].

package main

import (
	"fmt"
	"sort"
)

func main() {
	nums := []int{5, 2, 8, 1}
	sort.Slice(nums, func(i, j int) bool {
		return nums[i] > nums[j]
	})
	fmt.Println(nums)
}

Sorting Structs

sort.Slice shines with structs. You decide which field drives the order.

package main

import (
	"fmt"
	"sort"
)

type Person struct {
	Name string
	Age  int
}

func main() {
	people := []Person{{"Bob", 30}, {"Alice", 25}}
	sort.Slice(people, func(i, j int) bool {
		return people[i].Age < people[j].Age
	})
	fmt.Println(people)
}

Checking If Sorted

Helpers like sort.IntsAreSorted and sort.SliceIsSorted return true if a slice is already sorted, without changing it.

package main

import (
	"fmt"
	"sort"
)

func main() {
	nums := []int{1, 2, 3}
	fmt.Println(sort.IntsAreSorted(nums))
}

In-Place Modification

All these functions sort in place. They do not return a new slice. After calling sort.Ints(s), the variable s itself is reordered.

package main

import (
	"fmt"
	"sort"
)

func main() {
	s := []int{3, 1, 2}
	sort.Ints(s)
	fmt.Println("s is now:", s)
}

Choosing the Right Helper

Use the typed helpers (sort.Ints, sort.Strings, sort.Float64s) for simple slices. Reach for sort.Slice when you need a custom rule or sort structs.

sort.Ints - integers ascending
sort.Slice - anything, your rule

Quick Check

What does the less function in sort.Slice return?

Recap

You learned to sort with the sort package:

sort.Ints, sort.Strings, sort.Float64s for typed slices
sort.Slice with a less function for custom rules and structs
All sorting happens in place

Frequently asked questions

Is the “Sorting Slices” lesson free?

Yes — the full text of “Sorting Slices” is free to read here on the web, and the Go Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Go Academy course, upgrade to CoddyKit PRO.

What will I learn in “Sorting Slices”?

sort.Slice and helpers. You practise Go Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Go Academy?

No prior experience is required. Go Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Sorting Slices” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Go Academy lesson?

Yes. Every Go Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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