From 0459cd076494ab920a9672693d10b12ea21b54cf Mon Sep 17 00:00:00 2001
From: Thuc Le <ledongthuc@gmail.com>
Date: Wed, 5 Jan 2022 20:44:25 +0100
Subject: [PATCH] Add Sum() and Average()

---
 README.md       | 29 +++++++++++++++++++++++++++++
 average.go      | 14 ++++++++++++++
 average_test.go | 27 +++++++++++++++++++++++++++
 constraints.go  |  7 +++++++
 reduce.go       | 10 ++++++++++
 reduce_right.go |  5 +++++
 sum.go          |  9 +++++++++
 sum_test.go     | 21 +++++++++++++++++++++
 8 files changed, 122 insertions(+)
 create mode 100644 average.go
 create mode 100644 average_test.go
 create mode 100644 constraints.go
 create mode 100644 sum.go
 create mode 100644 sum_test.go

diff --git a/README.md b/README.md
index dffa936..f4474e4 100644
--- a/README.md
+++ b/README.md
@@ -17,7 +17,10 @@
    - [exist](#exist)
    - [include](#include)
    - [include some](#include-some)
+   - [sum](#sum)
+   - [average](#average)
 
+ - Support generic functions that fit with all your types.
  - The API and functions are inspired by Rust and Javascript.
 
 # Requirement
@@ -93,6 +96,7 @@ matchedStruct, index, err := Find(list, func(item MyStruct) bool {
    - list: source list we want to process.
    - initial value: the previous value that's used in the reducer call of the first element. At this time, previous = initial value, current = first element of the list.
    - reducer function: the function will run on all elements of the source list.
+ - Can use Reduce() or ReduceLeft() or FoldLeft()
 
 ```go
 // Sum
@@ -115,6 +119,7 @@ items := Reduce(testSource, []float64{}, func(previous []float64, current int, i
    - list: source list we want to process.
    - initial value: the previous value that's used in the reducer call of the last element. At this time, previous = initial value, current = last element of list.
    - reducer function: the function will run on all elements of the source list.
+ - Can use ReduceRight() or FoldRight()
 
 ```go
 // Reverse
@@ -245,6 +250,30 @@ result := IncludeSome(list, subList)
 fmt.Println("IncludeSome: ", result)
 ```
 
+## Sum
+
+![goterators-Sum](https://user-images.githubusercontent.com/1828895/148277403-70da16a7-5314-42d0-a9bf-c59bc3f0cba5.png)
+
+ - Sum plus all item from source list
+
+```go
+testSource := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}
+fmt.Println("Sum: ", Sum(testSource))
+```
+
+## Average
+
+![goterators-Average](https://user-images.githubusercontent.com/1828895/148277508-66a08f9e-22ec-4e04-8808-69bee8649871.png)
+
+ - Average sum of all the source list divided by the total number of source list
+ - We can use Average() or Mean()
+
+```go
+testSource := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}
+fmt.Println("Average: ", Average(testSource))
+fmt.Println("Mean: ", Mean(testSource))
+```
+
 # License
 
 MIT
diff --git a/average.go b/average.go
new file mode 100644
index 0000000..6d55bf1
--- /dev/null
+++ b/average.go
@@ -0,0 +1,14 @@
+package goterators
+
+// Average sum of all the source list divided by the total number of source list
+func Average[T Number](source []T) float64 {
+	var sum T
+	for _, item := range source {
+		sum += item
+	}
+	return float64(sum) / float64(len(source))
+}
+
+func Mean[T Number](source []T) float64 {
+	return Average(source)
+}
diff --git a/average_test.go b/average_test.go
new file mode 100644
index 0000000..d71da54
--- /dev/null
+++ b/average_test.go
@@ -0,0 +1,27 @@
+package goterators
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestAverage(t *testing.T) {
+	testSource := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}
+	expectedValue := 10.5
+
+	actutalValue := Average(testSource)
+	if actutalValue != expectedValue {
+		t.Errorf("Expected = %v , got = %v", expectedValue, actutalValue)
+	}
+
+	actutalValue = Mean(testSource)
+	if actutalValue != expectedValue {
+		t.Errorf("Expected = %v , got = %v", expectedValue, actutalValue)
+	}
+}
+
+func ExampleAverage() {
+	testSource := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}
+	fmt.Println("Average: ", Average(testSource))
+	fmt.Println("Mean: ", Mean(testSource))
+}
diff --git a/constraints.go b/constraints.go
new file mode 100644
index 0000000..cb33a71
--- /dev/null
+++ b/constraints.go
@@ -0,0 +1,7 @@
+package goterators
+
+import "constraints"
+
+type Number interface {
+	constraints.Integer | constraints.Float
+}
diff --git a/reduce.go b/reduce.go
index 4c1151c..34e24cc 100644
--- a/reduce.go
+++ b/reduce.go
@@ -13,3 +13,13 @@ func Reduce[T1 any, T2 any](source []T1, initialValue T2, reducer func(previousV
 	}
 	return output
 }
+
+// ReduceLeft is same with Reduce()
+func ReduceLeft[T1 any, T2 any](source []T1, initialValue T2, reducer func(previousValue T2, currentValue T1, currentIndex int, list []T1) T2) T2 {
+	return Reduce(source, initialValue, reducer)
+}
+
+// FoldLeft is same with Reduce()
+func FoldLeft[T1 any, T2 any](source []T1, initialValue T2, reducer func(previousValue T2, currentValue T1, currentIndex int, list []T1) T2) T2 {
+	return Reduce(source, initialValue, reducer)
+}
diff --git a/reduce_right.go b/reduce_right.go
index 9cd6ca5..3847e12 100644
--- a/reduce_right.go
+++ b/reduce_right.go
@@ -13,3 +13,8 @@ func ReduceRight[T1 any, T2 any](source []T1, initialValue T2, reducer func(prev
 	}
 	return output
 }
+
+// FoldRight is same with Reduce()
+func FoldRight[T1 any, T2 any](source []T1, initialValue T2, reducer func(previousValue T2, currentValue T1, currentIndex int, list []T1) T2) T2 {
+	return Reduce(source, initialValue, reducer)
+}
diff --git a/sum.go b/sum.go
new file mode 100644
index 0000000..37a190a
--- /dev/null
+++ b/sum.go
@@ -0,0 +1,9 @@
+package goterators
+
+// Sum plus all item from source list
+func Sum[T Number](source []T) (result T) {
+	for _, item := range source {
+		result += item
+	}
+	return result
+}
diff --git a/sum_test.go b/sum_test.go
new file mode 100644
index 0000000..a04ef81
--- /dev/null
+++ b/sum_test.go
@@ -0,0 +1,21 @@
+package goterators
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestSum(t *testing.T) {
+	testSource := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}
+	expectedValue := 210
+	actutalValue := Sum(testSource)
+
+	if actutalValue != expectedValue {
+		t.Errorf("Expected = %v , got = %v", expectedValue, actutalValue)
+	}
+}
+
+func ExampleSum() {
+	testSource := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20}
+	fmt.Println("Sum: ", Sum(testSource))
+}