Golang Sorting Slices

Sorting Slices

In Go, sorting a slice is often necessary when working with data that needs to be organized or structured for better usability, efficiency, or presentation. Here are some common scenarios where you might need to sort a slice:

Displaying Sorted Data

Improving Search Efficiency

Custom Ranking or Prioritization

Data Cleaning and Organization

SortFunc function

In order to sort a slice we can use the slices.SortFunc function.

The slices.SortFunc function receives a slice and a comp function in order to sort the values. This comp function should return -1 if a < b, 1 if a > b and 0 if the values are equals.

var mySlice []string

mySlice = append(mySlice, "A")
mySlice = append(mySlice, "B")
mySlice = append(mySlice, "C")
mySlice = append(mySlice, "Z")
mySlice = append(mySlice, "M")
mySlice = append(mySlice, "Y")
mySlice = append(mySlice, "P")

slices.SortFunc(mySlice, func(a, b string) int {
    return strings.Compare(a, b)
})

for _, v := range mySlice {
    fmt.Println(v)
}

>>> A
>>> B
>>> C
>>> M
>>> P
>>> Y
>>> Z

If we would like to sort a slice of integer, we could change the function this way:

var mySlice []int

mySlice = append(mySlice, 55)
mySlice = append(mySlice, 53)
mySlice = append(mySlice, 105)
mySlice = append(mySlice, 3)
mySlice = append(mySlice, 375)
mySlice = append(mySlice, 376)
mySlice = append(mySlice, 377)
mySlice = append(mySlice, 250)
mySlice = append(mySlice, 15)

slices.SortFunc(mySlice, func(a, b int) int {
    return a - b
})

for _, v := range mySlice {
    fmt.Println(v)
}

>>> 3
>>> 15
>>> 53
>>> 55
>>> 105
>>> 250
>>> 375
>>> 376
>>> 377

Sorting a map

If we need to sort a map, we can create a struct in order to hold the values of the map, and then we can sort a slice of this struct.

package main

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

func main() {
	fmt.Println("Starting")

	var myMap = map[string]int{
		"G": 7,
		"B": 2,
		"C": 3,
		"E": 5,
		"A": 1,
		"D": 4,
		"H": 8,
		"F": 6,
	}

	type kv struct {
		Key   string
		Value int
	}

	var kvSlice []kv
	for k, v := range myMap {
		kvSlice = append(kvSlice, kv{Key: k, Value: v})
	}

	for k, v := range kvSlice {
		fmt.Println(k, v)
	}

	fmt.Println("----------")

	slices.SortFunc(kvSlice, func(a, b kv) int {
		return strings.Compare(a.Key, b.Key)
	})

	for k, v := range kvSlice {
		fmt.Println(k, v)
	}

}

>>> 55
>>> 53
>>> 105
>>> 3
>>> 375
>>> 376
>>> 377
>>> 250
>>> 15
>>> ----------
>>> 3
>>> 15
>>> 53
>>> 55
>>> 105
>>> 250
>>> 375
>>> 376
>>> 377