如何根据 Map [ string ] int 的值对它进行排序？

For example:

package main


import (
"fmt"
"sort"
)


func main() {
m := map[string]int{"hello": 10, "foo": 20, "bar": 20}
n := map[int][]string{}
var a []int
for k, v := range m {
n[v] = append(n[v], k)
}
for k := range n {
a = append(a, k)
}
sort.Sort(sort.Reverse(sort.IntSlice(a)))
for _, k := range a {
for _, s := range n[k] {
fmt.Printf("%s, %d\n", s, k)
}
}
}

Playground

Output:

foo, 20
bar, 20
hello, 10

Found the answer on Golang-nuts by Andrew Gerrand

You can implement the sort interface by writing the len/less/swap functions

func rankByWordCount(wordFrequencies map[string]int) PairList{
pl := make(PairList, len(wordFrequencies))
i := 0
for k, v := range wordFrequencies {
pl[i] = Pair{k, v}
i++
}
sort.Sort(sort.Reverse(pl))
return pl
}


type Pair struct {
Key string
Value int
}


type PairList []Pair


func (p PairList) Len() int { return len(p) }
func (p PairList) Less(i, j int) bool { return p[i].Value < p[j].Value }
func (p PairList) Swap(i, j int){ p[i], p[j] = p[j], p[i] }

For the original post, please find it here https://groups.google.com/forum/#!topic/golang-nuts/FT7cjmcL7gw

There's a new sort.Slice function in go 1.8, so now this is simpler.

package main


import (
"fmt"
"sort"
)


func main() {
m := map[string]int{
"something": 10,
"yo":        20,
"blah":      20,
}


type kv struct {
Key   string
Value int
}


var ss []kv
for k, v := range m {
ss = append(ss, kv{k, v})
}


sort.Slice(ss, func(i, j int) bool {
return ss[i].Value > ss[j].Value
})


for _, kv := range ss {
fmt.Printf("%s, %d\n", kv.Key, kv.Value)
}
}

https://play.golang.org/p/y1_WBENH4N

Sort keys first by value and then iterate map:

package main


import (
"fmt"
"sort"
)


func main() {
counts := map[string]int{"hello": 10, "foo": 20, "bar": 20}


keys := make([]string, 0, len(counts))
for key := range counts {
keys = append(keys, key)
}
sort.Slice(keys, func(i, j int) bool { return counts[keys[i]] > counts[keys[j]] })


for _, key := range keys {
fmt.Printf("%s, %d\n", key, counts[key])
}
}

I often need to sort a map[string]int of something I’m counting and have been using the following.

func rankMapStringInt(values map[string]int) []string {
type kv struct {
Key   string
Value int
}
var ss []kv
for k, v := range values {
ss = append(ss, kv{k, v})
}
sort.Slice(ss, func(i, j int) bool {
return ss[i].Value > ss[j].Value
})
ranked := make([]string, len(values))
for i, kv := range ss {
ranked[i] = kv.Key
}
return ranked
}

Use it to iterate over the keys in order of value

values := map[string]int{"foo": 10, "bar": 20, "baz": 1}


for i, index := range rankMapStringInt(values) {
fmt.Printf("%3d: %s -> %d", i, index, values[index])
}

In my case, I was dealing with a program that I created. In this program, I created a Map just like you, with string and int. Then I discovered like you that Go doesn't really have a built-in way to sort something like this. I read the other answers and didn't really like what I read.

So I tried to think about the problem differently. Go can use sort.Ints with a slice. Also, Go can use sort.Slice with a custom comparator. So instead of creating a Map of string and int, I created a struct of string and int. Then you can sort:

package main


import (
"fmt"
"sort"
)


type file struct {
name string
size int
}


func main() {
a := []file{
{"april.txt", 9}, {"may.txt", 7},
}
sort.Slice(a, func (d, e int) bool {
return a[d].size < a[e].size
})
fmt.Println(a)
}

This will not work for everyone, because maybe you will be forced to deal with a map someone else created. But it was useful for me. Good part is, unlike all the other answers, this one uses no loops.