[Golang] Sort String by Character

Sort a string by character, i.e., convert the string to []rune and then sort the slice of runes in Go programming language. This problem is actually the same as sorting a slice of runes in nature.

We use sort package in Go standard library to help us sort []rune, converted from the string.

Go prior to 1.8

The steps:

Convert string to []rune
Define a new type ByRune, which is actually []rune. Implement Len, Swap, and Less methods of type ByRune.
Call sort.Sort to sort the slice of runes.
Convert []rune back to string and return the string.

Run Code on Go Playground

package main

import (
      "fmt"
      "sort"
)

type ByRune []rune

func (r ByRune) Len() int           { return len(r) }
func (r ByRune) Swap(i, j int)      { r[i], r[j] = r[j], r[i] }
func (r ByRune) Less(i, j int) bool { return r[i] < r[j] }

func StringToRuneSlice(s string) []rune {
      var r []rune
      for _, runeValue := range s {
              r = append(r, runeValue)
      }
      return r
}

func SortStringByCharacter(s string) string {
      var r ByRune = StringToRuneSlice(s)
      sort.Sort(r)
      return string(r)
}

func main() {
      fmt.Println(SortStringByCharacter("listen"))
      fmt.Println(SortStringByCharacter("silent"))
}

Go 1.8 or later

The sort package in Go 1.8 introduces new methods for sorting slices [6]. We can use sort.Slice method directly without defining a new type.

The steps:

Convert string to []rune
Define a less method and call sort.Slice with the slice of runes and the less method as parameters.
Convert []rune back to string and return the string.

Run Code on Go Playground

package main

import (
      "fmt"
      "sort"
)

func StringToRuneSlice(s string) []rune {
      var r []rune
      for _, runeValue := range s {
              r = append(r, runeValue)
      }
      return r
}

func SortStringByCharacter(s string) string {
      r := StringToRuneSlice(s)
      sort.Slice(r, func(i, j int) bool {
              return r[i] < r[j]
      })
      return string(r)
}

func main() {
      fmt.Println(SortStringByCharacter("listen"))
      fmt.Println(SortStringByCharacter("silent"))
}

Tested on:

Ubuntu Linux 17.04, Go 1.8.1
Go Playground

References:

[1]	golang sort string - Google search golang sort string - DuckDuckGo search golang sort string - Ecosia search golang sort string - Qwant search golang sort string - Bing search golang sort string - Yahoo search golang sort string - Baidu search golang sort string - Yandex search

[2]	string - Go sort a slice of runes? - Stack Overflow

[3]	Package sort - The Go Programming Language

[4]	[Golang] Check Whether Two Strings Are Anagram of Each Other

[5]	Strings, bytes, runes and characters in Go - The Go Blog

[6]	sort: make sorting easier, add Slice, SliceStable, SliceIsSorted, reflect.Swapper · Issue #16721 · golang/go · GitHub