golang sorting maps by value and returning a slice of keys

Golang 1.23 Added new slices functions to help sort. These are useful for sorting maps by values or by keys.

In my previous post I went through some examples about how to sort by the keys of a map and return an array of values.

This does the converse and I provide examples to sort by the values of a map and return an array of keys.

https://www.geeksforgeeks.org/how-to-sort-golang-map-by-keys-or-values/ was helpful to see how to do it using the sort package. When I looked at the api docs, it suggested using the slices package:

"Note: in many situations, the newer slices.SortStableFunc function is more ergonomic and runs faster."

// Sort by value with map[int]string and map[string]int

func main() {

fmt.Println("Start")

fmt.Println("Sorting by Value in a map with int keys and string values")

intStringMap := map[int]string{

22: "z",

111: "y",

3333: "x",

}

// 1) Using sort package

intKeys := slices.Collect(maps.Keys(intStringMap))

sort.SliceStable(intKeys, func(i, j int) bool {

return intStringMap[intKeys[i]] < intStringMap[intKeys[j]]

})

fmt.Println("1) Using sort package:", intKeys) // [3333 111 22]

// 2) Using slices package

intKeySlice := slices.Collect(maps.Keys(intStringMap))

slices.SortStableFunc(intKeySlice, func(a, b int) int {

return cmp.Compare(intStringMap[a], intStringMap[b])

})

fmt.Println("2) Sort Keys in place", intKeySlice) // [3333 111 22]

fmt.Println()

fmt.Println("Sorting by Value in a map with string keys and int values")

stringIntMap := map[string]int{

"z": 222,

"y": 11,

"x": 3333,

}

// 1) Using sort package. API says consider using slices package

stringKeys := slices.Collect(maps.Keys(stringIntMap))

sort.SliceStable(stringKeys, func(i, j int) bool {

return stringIntMap[stringKeys[i]] < stringIntMap[stringKeys[j]]

})

fmt.Println("1) Using sort package:", stringKeys) // [y z x]

// 2) returns a slice where the values are the keys of stringIntMap

// sorts the keys in place

keySlice := slices.Collect(maps.Keys(stringIntMap))

slices.SortStableFunc(keySlice, func(a, b string) int {

return cmp.Compare(stringIntMap[a], stringIntMap[b])

})

fmt.Printf("2) Sort In Place: %v\n", keySlice) // [y z x]

// 3) returns a slice where the values are the keys of stringIntMap

keys := maps.Keys(stringIntMap) // an Iter

keysSortedByValue := slices.SortedStableFunc(keys, func(a, b string) int {

return cmp.Compare(stringIntMap[a], stringIntMap[b])

})

fmt.Printf("3) New Variable: %v\n", keysSortedByValue) // [y z x]

// Output the keys and values

fmt.Println("Print the stringIntMap in order")

for _, k := range keysSortedByValue {

fmt.Printf("%s: %d\n", k, stringIntMap[k])

}

// y: 11

// z: 222

// x: 3333

fmt.Println("Done")

}