GO map按某字段排序

package main

import (
   "fmt"
   "sort"
)

type frequency struct {
   char string
   fre  int
}

func frequencies(s string) []frequency {
   m := make(map[string]int)
   for _, r := range s {
      m[string(r)]++
   }
   a := make([]frequency, 0, len(m))
   for c, f := range m {
      a = append(a, frequency{char: c, fre: f})
   }
   sort.Slice(a, func(i, j int) bool {
      return a[i].fre > a[j].fre
   })
   return a
}
func main() {
   str := "hiilovegogo"
   fmt.Printf(str)
   f := frequencies(str)
   fmt.Println(f)
}