chore: add maps.Flip

maps/transform.go

@@ -30,3 +30,14 @@ func KVs[K comparable, V any](in map[K]V) []any {
 	}
 	return out
 }
+
+// Flip will return a new map with the keys and values of the input map flipped.
+// That is, the keys of the input map will be the values of the output map and
+// the values of the input map will be the keys of the output map.
+func Flip[K comparable, V comparable](in map[K]V) map[V]K {
+	out := make(map[V]K, len(in))
+	for k, v := range in {
+		out[v] = k
+	}
+	return out
+}

maps/transform_test.go

@@ -70,3 +70,25 @@ func TestKVs(t *testing.T) {
 		}
 	}
 }
+
+func TestFlip(t *testing.T) {
+	t.Parallel()
+
+	a := map[string]int{
+		"a": 1,
+		"b": 2,
+		"c": 3,
+	}
+
+	vks := maps.Flip(a)
+	assert.Len(t, vks, len(a))
+	for k, v := range a {
+		assert.Contains(t, vks, v)
+		assert.Equal(t, k, vks[v])
+	}
+
+	for k, v := range vks {
+		assert.Contains(t, a, v)
+		assert.Equal(t, k, a[v])
+	}
+}