Add ElementsMatch, ElementsMatchBy

intersect.go

@@ -225,3 +225,45 @@ func WithoutNth[T comparable, Slice ~[]T](collection Slice, nths ...int) Slice {
 
 	return result
 }
+
+// ElementsMatch returns true if lists
+// contain the same set of elements (including empty set).
+//
+// If there are duplicate elements,
+// the number of appearances of each of them in both lists should match.
+func ElementsMatch[T comparable, Slice ~[]T](list1 Slice, list2 Slice) bool {
+	return ElementsMatchBy(list1, list2, func(item T) T { return item })
+}
+
+// ElementsMatchBy returns true if lists
+// contain the same set of elements' keys (including empty set).
+//
+// If there are duplicate keys,
+// the number of appearances of each of them in both lists should match.
+func ElementsMatchBy[T any, K comparable](list1 []T, list2 []T, iteratee func(item T) K) bool {
+	if len(list1) != len(list2) {
+		return false
+	}
+
+	if len(list1) == 0 {
+		return true
+	}
+
+	counters := make(map[K]int, len(list1))
+
+	for _, el := range list1 {
+		counters[iteratee(el)]++
+	}
+
+	for _, el := range list2 {
+		counters[iteratee(el)]--
+	}
+
+	for _, count := range counters {
+		if count != 0 {
+			return false
+		}
+	}
+
+	return true
+}

intersect_test.go

@@ -330,3 +330,19 @@ func TestWithoutNth(t *testing.T) {
 	nonempty := WithoutNth(allStrings)
 	is.IsType(nonempty, allStrings, "type preserved")
 }
+
+func TestElementsMatch(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	is.False(ElementsMatch([]int{}, []int{1}))
+	is.False(ElementsMatch([]int{1}, []int{2}))
+	is.False(ElementsMatch([]int{1}, []int{1, 2}))
+	is.False(ElementsMatch([]int{1, 1, 2}, []int{2, 2, 1}))
+
+	is.True(ElementsMatch([]int{}, nil))
+	is.True(ElementsMatch([]int{1}, []int{1}))
+	is.True(ElementsMatch([]int{1, 1}, []int{1, 1}))
+	is.True(ElementsMatch([]int{1, 2}, []int{2, 1}))
+	is.True(ElementsMatch([]int{1, 1, 2}, []int{1, 2, 1}))
+}