Feature/intersect by (#653)

* Update README.md

Fixed the error in the usage example of lo.Latest in readme.md

use []time.Time{…} (value of type []time.Time) as time.Time value in argument to lo.Latest

* Update README.md

* feature: add Mode function with tests and documentation

* feat: Add IntersectBy function and tests, supporting intersection by custom key sets

---------

Co-authored-by: Samuel Berthe <dev@samuel-berthe.fr>

intersect.go

@@ -170,6 +170,27 @@ func Intersect[T comparable, Slice ~[]T](lists ...Slice) Slice {
 	return Slice{}
 }
 
+// IntersectBy returns the intersection between two collections using a custom key selector function.
+// It preserves the order of elements from the second list (list2).
+func IntersectBy[T any, K comparable, Slice ~[]T](list1 Slice, list2 Slice, iteratee func(T) K) Slice {
+	result := make(Slice, 0)
+	seen := make(map[K]struct{})
+
+	for _, item := range list1 {
+		key := iteratee(item)
+		seen[key] = struct{}{}
+	}
+
+	for _, item := range list2 {
+		key := iteratee(item)
+		if _, exists := seen[key]; exists {
+			result = append(result, item)
+		}
+	}
+
+	return result
+}
+
 // Difference returns the difference between two collections.
 // The first value is the collection of elements absent from list2.
 // The second value is the collection of elements absent from list1.

intersect_test.go

@@ -1,6 +1,7 @@
 package lo
 
 import (
+	"strconv"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -204,6 +205,46 @@ func TestIntersect(t *testing.T) {
 	is.IsType(nonempty, allStrings, "type preserved")
 }
 
+func TestIntersectBy(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	type User struct {
+		ID   int
+		Name string
+	}
+
+	list1 := []User{
+		{ID: 1, Name: "Alice"},
+		{ID: 2, Name: "Bob"},
+		{ID: 3, Name: "Charlie"},
+	}
+
+	list2 := []User{
+		{ID: 2, Name: "Robert"},
+		{ID: 3, Name: "Charlie"},
+		{ID: 4, Name: "Alice"},
+	}
+
+	intersectByID := IntersectBy(list1, list2, func(u User) int {
+		return u.ID
+	})
+	is.Equal(intersectByID, []User{{ID: 2, Name: "Robert"}, {ID: 3, Name: "Charlie"}})
+	// output: [{2 Robert} {3 Charlie}]
+
+	intersectByName := IntersectBy(list1, list2, func(u User) string {
+		return u.Name
+	})
+	is.Equal(intersectByName, []User{{ID: 3, Name: "Charlie"}, {ID: 4, Name: "Alice"}})
+	// output: [{3 Charlie} {4 Alice}]
+
+	intersectByIDAndName := IntersectBy(list1, list2, func(u User) string {
+		return strconv.Itoa(u.ID) + u.Name
+	})
+	is.Equal(intersectByIDAndName, []User{{ID: 3, Name: "Charlie"}})
+	// output: [{3 Charlie}]
+}
+
 func TestDifference(t *testing.T) {
 	t.Parallel()
 	is := assert.New(t)