add SliceReduce and MapReduce methods

go.mod

@@ -0,0 +1,7 @@
+module github.com/DsXack/go
+
+require (
+	github.com/davecgh/go-spew v1.1.0
+	github.com/pmezard/go-difflib v1.0.0
+	github.com/stretchr/testify v1.2.2
+)

go.sum

@@ -0,0 +1,6 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=

reflect/collect/map_reduce.go

@@ -0,0 +1,24 @@
+package collect
+
+import "reflect"
+
+// MapReduce method reduces the map to a single value, passing the result of each iteration
+// into the subsequent iteration:
+func MapReduce(mapValue interface{}, initialValue interface{}, reduceFunc interface{}) interface{} {
+	refFunc := reflect.ValueOf(reduceFunc)
+	refMap := reflect.ValueOf(mapValue)
+
+	refInitialValue := reflect.ValueOf(initialValue)
+	refValue := reflect.New(refInitialValue.Type())
+	refValue.Elem().Set(refInitialValue)
+
+	for _, k := range refMap.MapKeys() {
+		v := refFunc.Call(
+			[]reflect.Value{refValue.Elem(), k, refMap.MapIndex(k)},
+		)[0]
+
+		refValue.Elem().Set(v)
+	}
+
+	return refValue.Elem().Interface()
+}

reflect/collect/map_reduce_test.go

@@ -0,0 +1,16 @@
+package collect
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestMapReduce(t *testing.T) {
+	res := MapReduce(
+		map[int]int{1: 1, 2: 2},
+		0,
+		func(accum int, key, value int) int { return accum + value },
+	).(int)
+
+	assert.Equal(t, 3, res)
+}

reflect/collect/slice_map_test.go

@@ -14,5 +14,5 @@ func TestSliceMap(t *testing.T) {
 		},
 	).([]string)
 
-	assert.ElementsMatch(t, res, []string{"1", "4", "9"})
+	assert.ElementsMatch(t, []string{"1", "4", "9"}, res)
 }

reflect/collect/slice_reduce.go

@@ -0,0 +1,23 @@
+package collect
+
+import "reflect"
+
+// SliceReduce method reduces the slice to a single value, passing the result of each iteration
+// into the subsequent iteration:
+func SliceReduce(value interface{}, initialValue interface{}, mapFunc interface{}) interface{} {
+	refFunc := reflect.ValueOf(mapFunc)
+	refSlice := reflect.ValueOf(value)
+
+	refInitialValue := reflect.ValueOf(initialValue)
+	refValue := reflect.New(refInitialValue.Type())
+	refValue.Elem().Set(refInitialValue)
+
+	for i := 0; i < refSlice.Len(); i += 1 {
+		v := refFunc.Call(
+			[]reflect.Value{refValue.Elem(), reflect.ValueOf(i), refSlice.Index(i)},
+		)[0]
+		refValue.Elem().Set(v)
+	}
+
+	return refValue.Elem().Interface()
+}

reflect/collect/slice_reduce_test.go

@@ -0,0 +1,16 @@
+package collect
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestSliceReduce(t *testing.T) {
+	res := SliceReduce(
+		[]int{1, 2, 3},
+		0,
+		func(accum, index, value int) int { return accum + value },
+	).(int)
+
+	assert.Equal(t, 6, res)
+}