fix(groupbymap): remove second iteratee and add test+example+doc

Author: samber

README.md

@@ -92,6 +92,7 @@ Supported helpers for slices:
 - [Uniq](#uniq)
 - [UniqBy](#uniqby)
 - [GroupBy](#groupby)
+- [GroupByMap](#groupbymap)
 - [Chunk](#chunk)
 - [PartitionBy](#partitionby)
 - [Flatten](#flatten)
@@ -566,6 +567,19 @@ lop.GroupBy([]int{0, 1, 2, 3, 4, 5}, func(i int) int {
 // map[int][]int{0: []int{0, 3}, 1: []int{1, 4}, 2: []int{2, 5}}
 ```
 
+### GroupByMap
+
+Returns an object composed of keys generated from the results of running each element of collection through iteratee.
+
+```go
+import lo "github.com/samber/lo"
+
+groups := lo.GroupByMap([]int{0, 1, 2, 3, 4, 5}, func(i int) (int, int) {
+    return i%3, i*2
+})
+// map[int][]int{0: []int{0, 6}, 1: []int{2, 8}, 2: []int{4, 10}}
+```
+
 ### Chunk
 
 Returns an array of elements split into groups the length of size. If array can't be split evenly, the final chunk will be the remaining elements.

slice.go

@@ -188,18 +188,15 @@ func GroupBy[T any, U comparable, Slice ~[]T](collection Slice, iteratee func(it
 	return result
 }
 
-
-
-// GroupByMapValues returns an object composed of keys generated from the results of running each element of collection through iterateeKey and values running each element through iterateeValue.
-func GroupByMapValues[K comparable, T any, V any](arr []T, iterateeKey func(T) K, iterateeValue func(T) V) map[K][]V {
+// GroupByMap returns an object composed of keys generated from the results of running each element of collection through iteratee.
+func GroupByMap[T any, K comparable, V any](arr []T, iteratee func(item T) (K, V)) map[K][]V {
 	result := map[K][]V{}
 
 	for _, item := range arr {
-		k := iterateeKey(item)
-		v := iterateeValue(item)
-
+		k, v := iteratee(item)
 		result[k] = append(result[k], v)
 	}
+
 	return result
 }
 

slice_example_test.go

@@ -165,6 +165,22 @@ func ExampleGroupBy() {
 	// [2 5]
 }
 
+func ExampleGroupByMap() {
+	list := []int{0, 1, 2, 3, 4, 5}
+
+	result := GroupByMap(list, func(i int) (int, int) {
+		return i % 3, i * 2
+	})
+
+	fmt.Printf("%v\n", result[0])
+	fmt.Printf("%v\n", result[1])
+	fmt.Printf("%v\n", result[2])
+	// Output:
+	// [0 6]
+	// [2 8]
+	// [4 10]
+}
+
 func ExampleChunk() {
 	list := []int{0, 1, 2, 3, 4}
 

slice_test.go

@@ -254,6 +254,22 @@ func TestGroupBy(t *testing.T) {
 	is.IsType(nonempty[42], allStrings, "type preserved")
 }
 
+func TestGroupByMap(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	result1 := GroupByMap([]int{0, 1, 2, 3, 4, 5}, func(i int) (int, string) {
+		return i % 3, strconv.Itoa(i)
+	})
+
+	is.Equal(len(result1), 3)
+	is.Equal(result1, map[int][]string{
+		0: {"0", "3"},
+		1: {"1", "4"},
+		2: {"2", "5"},
+	})
+}
+
 func TestChunk(t *testing.T) {
 	t.Parallel()
 	is := assert.New(t)