feat: add GroupWith func

slice/slice.go

@@ -253,6 +253,25 @@ func GroupBy[T any](slice []T, groupFn func(index int, t T) bool) ([]T, []T) {
 	return groupA, groupB
 }
 
+// GroupWith return a map composed of keys generated from the results of running each element of slice thru iteratee.
+func GroupWith[T any, U comparable](slice []T, iteratee func(T) U) map[U][]T {
+	if iteratee == nil {
+		panic("iteratee func is missing")
+	}
+
+	res := make(map[U][]T)
+
+	for _, v := range slice {
+		key := iteratee(v)
+		if _, ok := res[key]; !ok {
+			res[key] = []T{}
+		}
+		res[key] = append(res[key], v)
+	}
+
+	return res
+}
+
 // Find iterates over elements of slice, returning the first one that passes a truth test on predicate function.
 // If return T is nil then no items matched the predicate func
 func Find[T any](slice []T, predicate func(index int, t T) bool) (*T, bool) {

slice/slice_test.go

@@ -1,6 +1,7 @@
 package slice
 
 import (
+	"math"
 	"testing"
 
 	"github.com/duke-git/lancet/v2/internal"
@@ -142,6 +143,20 @@ func TestGroupBy(t *testing.T) {
 	assert.Equal(expectedOdd, odd)
 }
 
+func TestGroupWith(t *testing.T) {
+	nums := []float64{6.1, 4.2, 6.3}
+	floor := func(num float64) float64 {
+		return math.Floor(num)
+	}
+	expected := map[float64][]float64{
+		4: {4.2},
+		6: {6.1, 6.3},
+	}
+	actual := GroupWith(nums, floor)
+	assert := internal.NewAssert(t, "TestGroupWith")
+	assert.Equal(expected, actual)
+}
+
 func TestCount(t *testing.T) {
 	nums := []int{1, 2, 3, 4, 5, 6}
 	evenFunc := func(i, num int) bool {