Merge pull request #116 from vellotis/#50

Fixes issue #50

Author: thoas

README.rst

@@ -261,6 +261,26 @@ see also, typesafe implementations: FilterInt_, FilterInt64_, FilterFloat32_, Fi
 .. _FilterInt64: https://godoc.org/github.com/thoas/go-funk#FilterInt64
 .. _FilterString: https://godoc.org/github.com/thoas/go-funk#FilterString
 
+funk.Reduce
+...........
+
+Reduces an iteratee based on an accumulator function or operation rune for numbers.
+
+.. code-block:: go
+
+    // Using operation runes. '+' and '*' only supported.
+    r := funk.Reduce([]int{1, 2, 3, 4}, '+', float64(0)) // 10
+    r := funk.Reduce([]int{1, 2, 3, 4}, '*', 1) // 24
+
+    // Using accumulator function
+    r := funk.Reduce([]int{1, 2, 3, 4}, func(acc float64, num int) float64 {
+        return acc + float64(num)
+    }, float64(0)) // 10
+
+    r := funk.Reduce([]int{1, 2, 3, 4}, func(acc string, num int) string {
+        return acc + fmt.Sprint(num)
+    }, "") // "1234"
+
 funk.Find
 .........
 
@@ -318,7 +338,7 @@ Manipulates an iteratee (map, slice) and transforms it to another type:
     }) // map[string]string{"1": "Florent", "2": "Gilles"}
 
 funk.FlatMap
-........
+............
 
 Manipulates an iteratee (map, slice) and transforms it to to a flattened collection of another type:
 

builder.go

@@ -39,7 +39,7 @@ type Builder interface {
 	LastIndexOf(elem interface{}) int
 	NotEmpty() bool
 	Product() float64
-	Reduce(reduceFunc, acc interface{}) float64
+	Reduce(reduceFunc, acc interface{}) interface{}
 	Sum() float64
 	Type() reflect.Type
 	Value() interface{}

chain_builder.go

@@ -125,7 +125,7 @@ func (b *chainBuilder) NotEmpty() bool {
 func (b *chainBuilder) Product() float64 {
 	return Product(b.collection)
 }
-func (b *chainBuilder) Reduce(reduceFunc, acc interface{}) float64 {
+func (b *chainBuilder) Reduce(reduceFunc, acc interface{}) interface{} {
 	return Reduce(b.collection, reduceFunc, acc)
 }
 func (b *chainBuilder) Sum() float64 {

chain_builder_test.go

@@ -1012,6 +1012,11 @@ func TestChainReduce(t *testing.T) {
 			ReduceFunc: '*',
 			Acc:        1,
 		},
+		{
+			In:         []string{"1", "2", "3", "4"},
+			ReduceFunc: func(acc string, elem string) string { return acc + elem },
+			Acc:        "",
+		},
 	}
 
 	for idx, tc := range testCases {

lazy_builder.go

@@ -100,7 +100,7 @@ func (b *lazyBuilder) NotEmpty() bool {
 func (b *lazyBuilder) Product() float64 {
 	return Product(b.exec())
 }
-func (b *lazyBuilder) Reduce(reduceFunc, acc interface{}) float64 {
+func (b *lazyBuilder) Reduce(reduceFunc, acc interface{}) interface{} {
 	return Reduce(b.exec(), reduceFunc, acc)
 }
 func (b *lazyBuilder) Sum() float64 {

lazy_builder_test.go

@@ -1012,6 +1012,11 @@ func TestLazyReduce(t *testing.T) {
 			ReduceFunc: '*',
 			Acc:        1,
 		},
+		{
+			In:         []string{"1", "2", "3", "4"},
+			ReduceFunc: func(acc string, elem string) string { return acc + elem },
+			Acc:        "",
+		},
 	}
 
 	for idx, tc := range testCases {

reduce.go

@@ -6,7 +6,7 @@ import (
 
 // Reduce takes a collection and reduces it to a single value using a reduction
 // function (or a valid symbol) and an accumulator value.
-func Reduce(arr, reduceFunc, acc interface{}) float64 {
+func Reduce(arr, reduceFunc, acc interface{}) interface{} {
 	arrValue := redirectValue(reflect.ValueOf(arr))
 
 	if !IsIteratee(arrValue.Interface()) {
@@ -83,6 +83,5 @@ func Reduce(arr, reduceFunc, acc interface{}) float64 {
 		accValue = result[0]
 	}
 
-	resultInterface := accValue.Convert(returnType).Interface()
-	return resultInterface.(float64)
+	return accValue.Convert(returnType).Interface()
 }

reduce_test.go

@@ -12,19 +12,19 @@ func TestReduce(t *testing.T) {
 		Arr    interface{}
 		Func   interface{}
 		Acc    interface{}
-		Result float64
+		Result interface{}
 	}{
 		{
 			[]int{1, 2, 3, 4},
-			func(acc, elem int) int { return acc + elem },
+			func(acc, elem float64) float64 { return acc + elem },
 			0,
 			float64(10),
 		},
 		{
 			&[]int16{1, 2, 3, 4},
 			'+',
 			5,
-			float64(15),
+			int16(15),
 		},
 		{
 			[]float64{1.1, 2.2, 3.3},
@@ -36,14 +36,20 @@ func TestReduce(t *testing.T) {
 			&[]int{1, 2, 3, 5},
 			func(acc int8, elem int16) int32 { return int32(acc) * int32(elem) },
 			1,
-			float64(30),
+			int32(30),
 		},
 		{
 			[]interface{}{1, 2, 3.3, 4},
 			'*',
 			1,
 			float64(26.4),
 		},
+		{
+			[]string{"1", "2", "3", "4"},
+			func(acc string, elem string) string { return acc + elem },
+			"",
+			"1234",
+		},
 	}
 
 	for idx, test := range testCases {