sorting-by-func.go

package main

import (
	"fmt"
	"sort"
)

/*
Sometimes we’ll want to sort a collection by something other than its natural order.
For example, suppose we wanted to sort strings by their length instead of alphabetically.
Here’s an example of custom sorts in Go.
*/

// In order to sort by a custom function in Go,
// we need a corresponding type.
// Here we’ve created a byLength type that is just an alias for the builtin []string type.
type byLength []string

// We implement sort.Interface - Len, Less, and Swap -
// on our type so we can use the sort package’s generic Sort function.
//Len and Swap will usually be similar across types and Less will hold the actual custom sorting logic.
// In our case we want to sort in order of increasing string length, so we use len(s[i]) and len(s[j]) here.
func (s byLength) Len() int {
	return len(s)
}

func (s byLength) Swap(i, j int) {
	s[i], s[j] = s[j], s[i]
}

func (s byLength) Less(i, j int) bool {
	return len(s[i]) < len(s[j])
}

// SortByFunc illustrate sorting by function func
func SortByFunc() {
	// With all of this in place, we can now implement our custom sort
	//by casting the original fruits slice to byLength,
	// and then use sort.Sort on that typed slice.
	fruits := []string{"peach", "banana", "kiwi"}
	sort.Sort(byLength(fruits))
	fmt.Println(fruits)
}

// Running our program shows a list sorted by string length, as desired.
// By following this same pattern of creating a custom type,
// implementing the three Interface methods on that type,
// and then calling sort.Sort on a collection of that custom type,
// we can sort Go slices by arbitrary functions.