How to Sort a String-Integer Map by Value in Descending Order in Go?

Sorting a Map by its Values

Given a map of strings to integers, it is desirable to sort the map by its values in descending order.

Solution:

Implementing a custom sorting interface can achieve this functionality. The following code provides all the necessary functions to sort a map by its values:

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 example, using the given map:

m := map[string]int{"hello": 10, "foo": 20, "bar": 20}

The sorted output would be:

foo, 20
bar, 20
hello, 10

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