Slice: Add GroupBy func (#10)

Group by: split slice into two groups, applies on each slice element a
predicate func to categorize this element.

Changes

* Add groub by func
* Add test case for this func

README.md

@@ -412,6 +412,7 @@ func Unique(slice interface{}) interface{} //remove duplicate elements in slice
 func Union(slices ...interface{}) interface{} //Union creates a slice of unique values, in order, from all given slices. using == for equality comparisons.
 func UpdateByIndex(slice interface{}, index int, value interface{}) (interface{}, error) //update the slice element at index.
 func Without(slice interface{}, values ...interface{}) interface{} //creates a slice excluding all given values
+func GroupBy(slice, function interface{}) (interface{}, interface{}) // groups slice into two categories
 ```
 
 #### 10. strutil is for processing string

README_zh-CN.md

@@ -413,6 +413,7 @@ func Unique(slice interface{}) interface{} //去重切片
 func Union(slices ...interface{}) interface{} //slice并集, 去重
 func UpdateByIndex(slice interface{}, index int, value interface{}) (interface{}, error) //在切片中index位置更新value
 func Without(slice interface{}, values ...interface{}) interface{} //slice去除values
+func GroupBy(slice, function interface{}) (interface{}, interface{}) 
 ```
 
 #### 10. strutil字符串处理包

slice/slice.go

@@ -169,6 +169,32 @@ func Filter(slice, function interface{}) interface{} {
 	return res.Interface()
 }
 
+// GroupBy iterate over elements of the slice, each element will be group by criteria, returns two slices
+// The function signature should be func(index int, value interface{}) bool .
+func GroupBy(slice, function interface{}) (interface{}, interface{}) {
+	sv := sliceValue(slice)
+	fn := functionValue(function)
+
+	elemType := sv.Type().Elem()
+	if checkSliceCallbackFuncSignature(fn, elemType, reflect.ValueOf(true).Type()) {
+		panic("function param should be of type func(int, " + elemType.String() + ")" + reflect.ValueOf(true).Type().String())
+	}
+
+	groupB := reflect.MakeSlice(sv.Type(), 0, 0)
+	groupA := reflect.MakeSlice(sv.Type(), 0, 0)
+
+	for i := 0; i < sv.Len(); i++ {
+		flag := fn.Call([]reflect.Value{reflect.ValueOf(i), sv.Index(i)})[0]
+		if flag.Bool() {
+			groupA = reflect.Append(groupA, sv.Index(i))
+		} else {
+			groupB = reflect.Append(groupB, sv.Index(i))
+		}
+	}
+
+	return groupA.Interface(), groupB.Interface()
+}
+
 // Find iterates over elements of slice, returning the first one that passes a truth test on function.
 // The function signature should be func(index int, value interface{}) bool .
 func Find(slice, function interface{}) interface{} {

slice/slice_test.go

@@ -161,6 +161,30 @@ func TestFilter(t *testing.T) {
 
 }
 
+func TestGroupBy(t *testing.T) {
+	nums := []int{1, 2, 3, 4, 5, 6}
+	evenFunc := func(i, num int) bool {
+		return (num % 2) == 0
+	}
+	expectedEven := []int{2, 4, 6}
+	even, odd := GroupBy(nums, evenFunc)
+
+	t.Log("odd", odd)
+
+	t.Log("even", even)
+
+	if !reflect.DeepEqual(IntSlice(even), expectedEven) {
+		internal.LogFailedTestInfo(t, "GroupBy even", nums, expectedEven, even)
+		t.FailNow()
+	}
+
+	expectedOdd := []int{1, 3, 5}
+	if !reflect.DeepEqual(IntSlice(odd), expectedOdd) {
+		internal.LogFailedTestInfo(t, "GroupBy odd", nums, expectedOdd, odd)
+		t.FailNow()
+	}
+}
+
 func TestFind(t *testing.T) {
 	nums := []int{1, 2, 3, 4, 5}
 	even := func(i, num int) bool {