Proposal: Add MinByKey and MaxByKey

[eliaperantoni]

Say you have a collection and want to find the element that minimizes or maximizes a function.

For example, here I have a slice of person structs and am looking for the one for which the computeAge method returns the lowest value:

type person struct {
	name     string
	birthday time.Time
}

func (p *person) computeAge() int {
	age := time.Now().Year() - p.birthday.Year() - 1
	if p.birthday.YearDay() < time.Now().YearDay() {
		age += 1
	}
	return age
}

func main() {
	people := []person{
		{"Jordan", time.Date(1994, time.October, 2, 0, 0, 0, 0, time.UTC)},
		{"Emily", time.Date(1868, time.March, 26, 0, 0, 0, 0, time.UTC)},
		{"Micheal", time.Date(1999, time.June, 5, 0, 0, 0, 0, time.UTC)},
		{"Nikola", time.Date(2001, time.November, 16, 0, 0, 0, 0, time.UTC)},
		{"Rachel", time.Date(1993, time.April, 1, 0, 0, 0, 0, time.UTC)},
	}

	youngest := lo.MinBy(people, func(a, b person) bool {
		return a.computeAge() < b.computeAge()
	})
	fmt.Println(youngest.name)
}

Using MinBy like this results in 8 calls to computeAge where 5 should have sufficed. Using a custom keying function with MinBy results in many more calls than necessary.

---

I propose adding a MinByKey and MaxByKey functions that apply the custom keying function to all elements and then return the one that minimizes/maximizes it.

The signatures would be:

func MinByKey[T any, K constraints.Ordered](collection []T, key func(T) K) T
func MaxByKey[T any, K constraints.Ordered](collection []T, key func(T) K) T

Would this contribution be appreciated @samber ?