slices: add Partition

Partition split the original slice into two slice.

Fixes #67326.

Author: leaxoy

api/next/67326.txt

@@ -0,0 +1 @@
+pkg slices, func Partition[$0 interface{ ~[]$1 }, $1 interface{}]($0, func($1) bool) ([]$1, []$1) #67326

doc/next/6-stdlib/99-minor/slices/67326.md

@@ -0,0 +1,4 @@
+The [Partition] function split original slice into two sub-slices
+by given predicate.
+The elements in the first slice all satisfy the predicate.
+The elements of the second slice none satisfy the predicate.

src/slices/example_test.go

@@ -411,3 +411,13 @@ func ExampleChunk() {
 	// [{Bob 5} {Vera 24}]
 	// [{Zac 15}]
 }
+
+func ExamplePartition() {
+	truthSlice, falseSlice := Partition([]int{1, 2, 3, 4, 5, 6}, func(x int) bool { return x%2 == 0 })
+	fmt.Println(truthSlice)
+	fmt.Println(falseSlice)
+
+	// Output:
+	// [2 4 6]
+	// [1 3 5]
+}

src/slices/slices.go

@@ -506,3 +506,19 @@ func Repeat[S ~[]E, E any](x S, count int) S {
 	}
 	return newslice
 }
+
+// Partition split the original slice into two slice.
+// The elements of the first slice all satisfy the predicate.
+// The elements of the second slice none satisfy the predicate.
+func Partition[Slice ~[]E, E any](s Slice, f func(E) bool) ([]E, []E) {
+	truthSlice := make([]E, 0)
+	falseSlice := make([]E, 0)
+	for _, x := range s {
+		if f(x) {
+			truthSlice = append(truthSlice, x)
+		} else {
+			falseSlice = append(falseSlice, x)
+		}
+	}
+	return truthSlice, falseSlice
+}

src/slices/slices_test.go

@@ -1450,3 +1450,37 @@ func TestRepeatPanics(t *testing.T) {
 		}
 	}
 }
+
+func TestPartition(t *testing.T) {
+	tests := []struct {
+		name       string
+		original   []int
+		truthSlice []int
+		falseSlice []int
+		predicate  func(int) bool
+	}{
+		{
+			name:       "split odd & even",
+			original:   []int{1, 2, 3, 4, 5, 6},
+			truthSlice: []int{1, 3, 5},
+			falseSlice: []int{2, 4, 6},
+			predicate:  func(x int) bool { return x%2 == 1 },
+		},
+		{
+			name:       "split by pivot",
+			original:   []int{1, 10, 100, 1000, 10000},
+			truthSlice: []int{1, 10},
+			falseSlice: []int{100, 1000, 10000},
+			predicate:  func(x int) bool { return x < 100 },
+		},
+	}
+	for _, testCase := range tests {
+		truthSlice, falseSlice := Partition(testCase.original, testCase.predicate)
+		if !Equal(truthSlice, testCase.truthSlice) {
+			t.Errorf("Partition %s truth failed", testCase.name)
+		}
+		if !Equal(falseSlice, testCase.falseSlice) {
+			t.Errorf("Parition %s false failed", testCase.name)
+		}
+	}
+}