How Do I Sort a Map by Its Values in Descending Order?

How to Sort a Map by Its Values

This question arises when dealing with a map where the goal is to sort the key-value pairs based on the values in descending order. For example, given a map like:

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

One may want to print the sorted pairs as follows:

foo, 20
bar, 20
hello, 10

Solution

A solution to this problem is to implement the sort interface by providing the necessary len, less, and swap functions. Here's an example implementation:

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] }

To use this function, pass the map as an argument to rankByWordCount, which will return a sorted list of the key-value pairs. You can then iterate over the list to print the sorted results.

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