How can I sort a Map[string]int by its values?

Solution 1:

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

Solution 2:

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

Solution 3:

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

Solution 4:

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])
    }
}