add a unique function

[roosteracham]

In daily development, the Map, Filter, and Reduce functions provided by FP are indeed very useful, but there may be identical elements in the arrays or slices used in business, so I have to deduplicate the arrays. Because FP does not provide deduplication functionality, I can only use the closure function to deduplicate when writing the Map myself, which is not very convenient. So I wrote functions for array and slice deduplication.

[roosteracham]

package fp

// Calls a defined by function on each element of an array, and returns an array with all element distinct.
func Unique[T any, K comparable](by func(T) K) func([]T) []T {

return func(xs []T) []T {
	result := make([]T, 0, len(xs))
	// unique map
	m := make(map[K]struct{}, len(xs))

	for _, item := range xs {
		key := by(item)
		if _, ok := m[key]; ok {
			continue
		}

		m[key] = struct{}{}
		result = append(result, item)
	}

	return result
}

}

[roosteracham]

package fp

import (
"testing"

"github.com/repeale/fp-go/lambda"

)

func TestUnique(t *testing.T) {
// Test : get unique values

res := Unique(lambda.Identify[int])([]int{1, 2, 3, 3})

if len(res) != 3 {
	t.Error("Unique should return unique values")
}

}

func TestUnique2(t *testing.T) {
// Test : get unique values

res := Pipe3(
	Map(add1),
	Filter(func(x int) bool {
		return x % 2 == 0
	}),
	Unique(lambda.Identify[int]),
)([]int{1, 2, 3, 3})

if len(res) != 2 {
	t.Error("Unique should return unique values")
}

}