GroupByDynamic operator

README.md

@@ -438,6 +438,7 @@ How to use the [assert API](doc/assert.md) to write unit tests while using RxGo.
 * [Buffer](doc/buffer.md) — periodically gather items from an Observable into bundles and emit these bundles rather than emitting the items one at a time
 * [FlatMap](doc/flatmap.md) — transform the items emitted by an Observable into Observables, then flatten the emissions from those into a single Observable
 * [GroupBy](doc/groupby.md) — divide an Observable into a set of Observables that each emit a different group of items from the original Observable, organized by key
+* [GroupByDynamic](doc/groupbydynamic.md) — divide an Observable into a dynamic set of Observables that each emit GroupedObservables from the original Observable, organized by key
 * [Map](doc/map.md) — transform the items emitted by an Observable by applying a function to each item
 * [Marshal](doc/marshal.md) — transform the items emitted by an Observable by applying a marshalling function to each item
 * [Scan](doc/scan.md) — apply a function to each item emitted by an Observable, sequentially, and emit each successive value

doc/groupby.md

@@ -4,6 +4,8 @@
 
 Divide an Observable into a set of Observables that each emit a different group of items from the original Observable, organized by key.
 
+It requires to pass the length of the set. If we require a dynamic set, we need to use [GroupByDynamic](groupbydynamic.md) instead.
+
 ![](http://reactivex.io/documentation/operators/images/groupBy.c.png)
 
 ## Example

doc/groupbydynamic.md

@@ -0,0 +1,58 @@
+# GroupBy Operator
+
+## Overview
+
+Divides an Observable into a dynamic set of Observables that each emit GroupedObservable from the original Observable, organized by key.
+
+`GroupByDyDynamic` differs from [GroupBy](groupby.md) in the sense that it does not require to pass the set length. 
+
+![](http://reactivex.io/documentation/operators/images/groupBy.c.png)
+
+## Example
+
+```go
+count := 3
+observable := rxgo.Range(0, 10).GroupByDynamic(func(item rxgo.Item) int {
+    return item.V.(int) % count
+}, rxgo.WithBufferedChannel(10))
+
+for i := range observable.Observe() {
+    groupedObservable := i.V.(rxgo.GroupedObservable)
+    fmt.Printf("New observable: %d\n", groupedObservable.Key)
+
+    for i := range groupedObservable.Observe() {
+        fmt.Printf("item: %v\n", i.V)
+    }
+}
+```
+
+Output:
+
+```
+New observable: 0
+item: 0
+item: 3
+item: 6
+item: 9
+New observable: 1
+item: 1
+item: 4
+item: 7
+item: 10
+New observable: 2
+item: 2
+item: 5
+item: 8
+```
+
+## Options
+
+* [WithBufferedChannel](options.md#withbufferedchannel)
+
+* [WithContext](options.md#withcontext)
+
+* [WithObservationStrategy](options.md#withobservationstrategy)
+
+* [WithErrorStrategy](options.md#witherrorstrategy)
+
+* [WithPublishStrategy](options.md#withpublishstrategy)

go.sum

@@ -4,8 +4,10 @@ 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/emirpasic/gods v1.12.0 h1:QAUIPSaCu4G+POclxeqb3F+WPpdKqFGlw36+yOzGlrg=
 github.com/emirpasic/gods v1.12.0/go.mod h1:YfzfFFoVP/catgzJb4IKIqXjX78Ha8FMSDh3ymbK86o=
+github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
@@ -31,6 +33,7 @@ golang.org/x/tools v0.0.0-20191108193012-7d206e10da11/go.mod h1:b+2E5dAYhXwXZwtn
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

observable.go

@@ -1,3 +1,4 @@
+// Package rxgo is the main RxGo package.
 package rxgo
 
 import (
@@ -44,6 +45,7 @@ type Observable interface {
 	FlatMap(apply ItemToObservable, opts ...Option) Observable
 	ForEach(nextFunc NextFunc, errFunc ErrFunc, completedFunc CompletedFunc, opts ...Option) Disposed
 	GroupBy(length int, distribution func(Item) int, opts ...Option) Observable
+	GroupByDynamic(distribution func(Item) int, opts ...Option) Observable
 	IgnoreElements(opts ...Option) Observable
 	Join(joiner Func2, right Observable, timeExtractor func(interface{}) time.Time, window Duration, opts ...Option) Observable
 	Last(opts ...Option) OptionalSingle
@@ -179,7 +181,7 @@ func observable(iterable Iterable, operatorFactory func() operator, forceSeq, by
 						runParallel(ctx, next, observe, operatorFactory, bypassGather, option, mergedOptions...)
 					}
 				}()
-				runFirstItem(ctx, f, firstItemIDCh, observe, next, operatorFactory, bypassGather, option, mergedOptions...)
+				runFirstItem(ctx, f, firstItemIDCh, observe, next, operatorFactory, option, mergedOptions...)
 				return next
 			}),
 		}
@@ -383,7 +385,7 @@ func runParallel(ctx context.Context, next chan Item, observe <-chan Item, opera
 	}()
 }
 
-func runFirstItem(ctx context.Context, f func(interface{}) int, notif chan Item, observe <-chan Item, next chan Item, operatorFactory func() operator, bypassGather bool, option Option, opts ...Option) {
+func runFirstItem(ctx context.Context, f func(interface{}) int, notif chan Item, observe <-chan Item, next chan Item, operatorFactory func() operator, option Option, opts ...Option) {
 	go func() {
 		op := operatorFactory()
 		stopped := false

observable_operator.go

@@ -1320,6 +1320,57 @@ func (o *ObservableImpl) GroupBy(length int, distribution func(Item) int, opts .
 	}
 }
 
+// GroupedObservable is the observable type emitted by the GroupByDynamic operator.
+type GroupedObservable struct {
+	Observable
+	// Key is the distribution key
+	Key int
+}
+
+// GroupByDynamic divides an Observable into a dynamic set of Observables that each emit GroupedObservable from the original Observable, organized by key.
+func (o *ObservableImpl) GroupByDynamic(distribution func(Item) int, opts ...Option) Observable {
+	option := parseOptions(opts...)
+	next := option.buildChannel()
+	ctx := option.buildContext()
+	chs := make(map[int]chan Item)
+
+	go func() {
+		observe := o.Observe(opts...)
+	loop:
+		for {
+			select {
+			case <-ctx.Done():
+				break loop
+			case i, ok := <-observe:
+				if !ok {
+					break loop
+				}
+				idx := distribution(i)
+				ch, contains := chs[idx]
+				if !contains {
+					ch = option.buildChannel()
+					chs[idx] = ch
+					Of(GroupedObservable{
+						Observable: &ObservableImpl{
+							iterable: newChannelIterable(ch),
+						},
+						Key: idx,
+					}).SendContext(ctx, next)
+				}
+				i.SendContext(ctx, ch)
+			}
+		}
+		for _, ch := range chs {
+			close(ch)
+		}
+		close(next)
+	}()
+
+	return &ObservableImpl{
+		iterable: newChannelIterable(next),
+	}
+}
+
 // Last returns a new Observable which emit only last item.
 // Cannot be run in parallel.
 func (o *ObservableImpl) Last(opts ...Option) OptionalSingle {
@@ -1682,7 +1733,6 @@ func (op *repeatOperator) end(ctx context.Context, dst chan<- Item) {
 	for {
 		select {
 		default:
-			break
 		case <-ctx.Done():
 			return
 		}
@@ -2241,7 +2291,7 @@ func (o *ObservableImpl) StartWith(iterable Iterable, opts ...Option) Observable
 
 // SumFloat32 calculates the average of float32 emitted by an Observable and emits a float32.
 func (o *ObservableImpl) SumFloat32(opts ...Option) OptionalSingle {
-	return o.Reduce(func(_ context.Context, acc interface{}, elem interface{}) (interface{}, error) {
+	return o.Reduce(func(_ context.Context, acc, elem interface{}) (interface{}, error) {
 		if acc == nil {
 			acc = float32(0)
 		}
@@ -2267,7 +2317,7 @@ func (o *ObservableImpl) SumFloat32(opts ...Option) OptionalSingle {
 
 // SumFloat64 calculates the average of float64 emitted by an Observable and emits a float64.
 func (o *ObservableImpl) SumFloat64(opts ...Option) OptionalSingle {
-	return o.Reduce(func(_ context.Context, acc interface{}, elem interface{}) (interface{}, error) {
+	return o.Reduce(func(_ context.Context, acc, elem interface{}) (interface{}, error) {
 		if acc == nil {
 			acc = float64(0)
 		}
@@ -2295,7 +2345,7 @@ func (o *ObservableImpl) SumFloat64(opts ...Option) OptionalSingle {
 
 // SumInt64 calculates the average of integers emitted by an Observable and emits an int64.
 func (o *ObservableImpl) SumInt64(opts ...Option) OptionalSingle {
-	return o.Reduce(func(_ context.Context, acc interface{}, elem interface{}) (interface{}, error) {
+	return o.Reduce(func(_ context.Context, acc, elem interface{}) (interface{}, error) {
 		if acc == nil {
 			acc = int64(0)
 		}

observable_operator_bench_test.go

@@ -63,7 +63,7 @@ func Benchmark_Reduce_Sequential(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		b.StopTimer()
 		obs := Range(0, benchNumberOfElementsSmall, WithBufferedChannel(benchChannelCap)).
-			Reduce(func(_ context.Context, acc interface{}, elem interface{}) (interface{}, error) {
+			Reduce(func(_ context.Context, acc, elem interface{}) (interface{}, error) {
 				// Simulate a blocking IO call
 				time.Sleep(5 * time.Millisecond)
 				if a, ok := acc.(int); ok {
@@ -84,7 +84,7 @@ func Benchmark_Reduce_Parallel(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		b.StopTimer()
 		obs := Range(0, benchNumberOfElementsSmall, WithBufferedChannel(benchChannelCap)).
-			Reduce(func(_ context.Context, acc interface{}, elem interface{}) (interface{}, error) {
+			Reduce(func(_ context.Context, acc, elem interface{}) (interface{}, error) {
 				// Simulate a blocking IO call
 				time.Sleep(5 * time.Millisecond)
 				if a, ok := acc.(int); ok {