From c01c9d14b4a62b6c7d299ca421a1b7982259641c Mon Sep 17 00:00:00 2001
From: dudaodong <lanliddd.2007@163.com>
Date: Tue, 4 Apr 2023 17:54:54 +0800
Subject: [PATCH] feat: add ReduceRight

---
 docs/slice.md               | 32 +++++++++++++++++++++++++++++++-
 docs/slice_zh-CN.md         | 31 ++++++++++++++++++++++++++++++-
 slice/slice.go              | 12 ++++++++++++
 slice/slice_example_test.go | 11 +++++++++++
 slice/slice_test.go         | 12 +++++++++++-
 5 files changed, 95 insertions(+), 3 deletions(-)

diff --git a/docs/slice.md b/docs/slice.md
index bec43ce..b3e0f3c 100644
--- a/docs/slice.md
+++ b/docs/slice.md
@@ -64,6 +64,7 @@ import (
 -   [Reverse](#Reverse)
 -   [Reduce](#Reduce)
 -   [ReduceBy](#ReduceBy)
+-   [ReduceRight](#ReduceRight)
 -   [Replace](#Replace)
 -   [ReplaceAll](#ReplaceAll)
 -   [Repeat](#Repeat)
@@ -1505,7 +1506,6 @@ func main() {
 }
 ```
 
-
 ### <span id="ReduceBy">ReduceBy</span>
 
 <p>Produces a value from slice by accumulating the result of each element as passed through the reducer function.</p>
@@ -1542,6 +1542,36 @@ func main() {
 }
 ```
 
+### <span id="ReduceRight">ReduceRight</span>
+
+<p>ReduceRight is like ReduceBy, but it iterates over elements of slice from right to left.</p>
+
+<b>Signature:</b>
+
+```go
+func ReduceRight[T any, U any](slice []T, initial U, reducer func(index int, item T, agg U) U) U
+```
+
+<b>Example:</b>
+
+```go
+import (
+    "fmt"
+    "github.com/duke-git/lancet/v2/slice"
+)
+
+func main() {
+    result := slice.ReduceRight([]int{1, 2, 3, 4}, "", func(_ int, item int, agg string) string {
+        return agg + fmt.Sprintf("%v", item)
+    })
+
+    fmt.Println(result)
+
+    // Output:
+    // 4321
+}
+```
+
 ### <span id="Replace">Replace</span>
 
 <p>Returns a copy of the slice with the first n non-overlapping instances of old replaced by new.</p>
diff --git a/docs/slice_zh-CN.md b/docs/slice_zh-CN.md
index ef92c16..0d98644 100644
--- a/docs/slice_zh-CN.md
+++ b/docs/slice_zh-CN.md
@@ -64,6 +64,7 @@ import (
 -   [Reverse](#Reverse)
 -   [Reduce](#Reduce)
 -   [ReduceBy](#ReduceBy)
+-   [ReduceRight](#ReduceRight)
 -   [Replace](#Replace)
 -   [ReplaceAll](#ReplaceAll)
 -   [Repeat](#Repeat)
@@ -1506,7 +1507,6 @@ func main() {
 }
 ```
 
-
 ### <span id="ReduceBy">ReduceBy</span>
 
 <p>对切片中执行reduce操作。</p>
@@ -1543,6 +1543,35 @@ func main() {
 }
 ```
 
+### <span id="ReduceRight">ReduceRight</span>
+
+<p>类似ReduceBy操作，迭代切片元素顺序从右至左。</p>
+
+<b>函数签名:</b>
+
+```go
+func ReduceRight[T any, U any](slice []T, initial U, reducer func(index int, item T, agg U) U) U
+```
+
+<b>示例:</b>
+
+```go
+import (
+    "fmt"
+    "github.com/duke-git/lancet/v2/slice"
+)
+
+func main() {
+    result := slice.ReduceRight([]int{1, 2, 3, 4}, "", func(_ int, item int, agg string) string {
+        return agg + fmt.Sprintf("%v", item)
+    })
+
+    fmt.Println(result)
+
+    // Output:
+    // 4321
+}
+```
 
 ### <span id="Replace">Replace</span>
 
diff --git a/slice/slice.go b/slice/slice.go
index 75f4396..39ea647 100644
--- a/slice/slice.go
+++ b/slice/slice.go
@@ -504,6 +504,18 @@ func ReduceBy[T any, U any](slice []T, initial U, reducer func(index int, item T
 	return accumulator
 }
 
+// ReduceRight is like ReduceBy, but it iterates over elements of slice from right to left.
+// Play: todo
+func ReduceRight[T any, U any](slice []T, initial U, reducer func(index int, item T, agg U) U) U {
+	accumulator := initial
+
+	for i := len(slice) - 1; i >= 0; i-- {
+		accumulator = reducer(i, slice[i], accumulator)
+	}
+
+	return accumulator
+}
+
 // Replace returns a copy of the slice with the first n non-overlapping instances of old replaced by new.
 // Play: https://go.dev/play/p/P5mZp7IhOFo
 func Replace[T comparable](slice []T, old T, new T, n int) []T {
diff --git a/slice/slice_example_test.go b/slice/slice_example_test.go
index 74ad4c7..d8d3a67 100644
--- a/slice/slice_example_test.go
+++ b/slice/slice_example_test.go
@@ -477,6 +477,17 @@ func ExampleReduceBy() {
 	// 1234
 }
 
+func ExampleReduceRight() {
+	result := ReduceRight([]int{1, 2, 3, 4}, "", func(_ int, item int, agg string) string {
+		return agg + fmt.Sprintf("%v", item)
+	})
+
+	fmt.Println(result)
+
+	// Output:
+	// 4321
+}
+
 func ExampleReplace() {
 	strs := []string{"a", "b", "c", "a"}
 
diff --git a/slice/slice_test.go b/slice/slice_test.go
index e15c0ad..805403b 100644
--- a/slice/slice_test.go
+++ b/slice/slice_test.go
@@ -406,7 +406,7 @@ func TestReduce(t *testing.T) {
 }
 
 func TestReduceBy(t *testing.T) {
-	assert := internal.NewAssert(t, "TestReduce2")
+	assert := internal.NewAssert(t, "TestReduceBy")
 
 	result1 := ReduceBy([]int{1, 2, 3, 4}, 0, func(_ int, item int, agg int) int {
 		return agg + item
@@ -421,6 +421,16 @@ func TestReduceBy(t *testing.T) {
 
 }
 
+func TestReduceRight(t *testing.T) {
+	assert := internal.NewAssert(t, "ReduceRight")
+
+	result := ReduceRight([]int{1, 2, 3, 4}, "", func(_ int, item int, agg string) string {
+		return agg + fmt.Sprintf("%v", item)
+	})
+
+	assert.Equal("4321", result)
+}
+
 func TestIntSlice(t *testing.T) {
 	var nums []any
 	nums = append(nums, 1, 2, 3)