GroupBy implementation in Golang for string slices

GroupBy.go

func GroupBy(slice []string, groupFn func(string) string) map[string][]string {
	groups := make(map[string][]string)
	for _, elem := range slice {
		elementKey := groupFn(elem)
		existing, present := groups[elementKey]
		if !present {
			existing = []string{}
		}
		existing = append(existing, elem)
		groups[elementKey] = existing
	}
	return groups
}

Its perfect, making it a bit concise

func GroupBy(slice []string, groupFn func(string) string) map[string][]string {
	groups := map[string][]string{}
	for _, elem := range slice {
		var elementKey string
		elementKey = groupFn(elem)
		if existing, present := groups[elementKey]; !present {
			groups[elementKey] = []string{elem}
		} else {
			groups[elementKey] = append(existing, elem)
		}
	}
	return groups
}

Cache to make it faster, if elements are repeated cache makes it faster

func GroupBy(slice []string, groupFn func(string) string) map[string][]string {
	groups := map[string][]string{}
	cache := map[string]string{}
	for _, elem := range slice {
		var elementKey string
		if val, ok := cache[elem]; ok {
			elementKey = val
		} else {
			elementKey = groupFn(elem)
			cache[elem] = elementKey
		}
		if existing, present := groups[elementKey]; !present {
			groups[elementKey] = []string{elem}
		} else {
			groups[elementKey] = append(existing, elem)
		}
	}
	return groups
}

Did a bench and the cache does it make it faster. Can use thread safe sync maps and use waitgroups to make it even faster

Can use thread safe sync maps and use waitgroups to make it even faster
@karthikcru Wouldn't locks make it slow? 🤔

If we prealloc the slices used to store the groups, but this increases the space to n^2, appending to non prealloc slice is costly

@ashwanthkumar The locks are on the group rather than the entire map, so it essentially is wasting resources in the thread waiting for the lock to get free if it writes into the same group, but if they write to different groups it does get faster right ? Am I saying this right ?