[BEAM-10235] Adding a CountElms transform to the Go SDK.

This transform counts the number of elements in a PTransform.

sdks/go/pkg/beam/transforms/stats/count.go

@@ -18,18 +18,36 @@ package stats
 
 import (
  "github.com/apache/beam/sdks/go/pkg/beam"
+ "github.com/apache/beam/sdks/go/pkg/beam/core/typex"
 )
 
-// Count counts the number of elements in a collection. It expects a
-// PCollection<T> as input and returns a PCollection<KV<T,int>>. T's encoding
-// must be a well-defined injection.
+// Count counts the number of appearances of each element in a collection. It
+// expects a PCollection<T> as input and returns a PCollection<KV<T,int>>. T's
+// encoding must be deterministic so it is valid as a key.
 func Count(s beam.Scope, col beam.PCollection) beam.PCollection {
  s = s.Scope("stats.Count")
 
- pre := beam.ParDo(s, mapFn, col)
+ pre := beam.ParDo(s, keyedCountFn, col)
  return SumPerKey(s, pre)
 }
 
-func mapFn(elm beam.T) (beam.T, int) {
+func keyedCountFn(elm beam.T) (beam.T, int) {
  return elm, 1
 }
+
+// CountElms counts the number of elements in a collection. It expects a
+// PCollection<T> as input and returns a PCollection<int> of one element
+// containing the count.
+func CountElms(s beam.Scope, col beam.PCollection) beam.PCollection {
+ s = s.Scope("stats.CountElms")
+
+ if typex.IsKV(col.Type()) {
+ col = beam.DropKey(s, col)
+ }
+ pre := beam.ParDo(s, countFn, col)
+ return Sum(s, pre)
+}
+
+func countFn(_ beam.T) int {
+ return 1
+}

sdks/go/pkg/beam/transforms/stats/count_test.go

@@ -16,6 +16,7 @@
 package stats
 
 import (
+ "fmt"
  "testing"
 
  "github.com/apache/beam/sdks/go/pkg/beam"
@@ -67,3 +68,53 @@ func TestCountInt(t *testing.T) {
  }
  }
 }
+
+// TestCountElms verifies that CountElms works correctly with PCollections of
+// various types, including keyed and unkeyed elements.
+func TestCountElms(t *testing.T) {
+
+ tests := []struct {
+ name string
+ in func(s beam.Scope) beam.PCollection
+ count int
+ }{
+ {
+ name: "single",
+ in: func(s beam.Scope) beam.PCollection {
+ return beam.Create(s, 1)
+ },
+ count: 1,
+ },
+ {
+ name: "multiple",
+ in: func(s beam.Scope) beam.PCollection {
+ return beam.Create(s, "one", "two", "three")
+ },
+ count: 3,
+ },
+ {
+ name: "keyed",
+ in: func(s beam.Scope) beam.PCollection {
+ vals := beam.Create(s, 1.0, 2.0, 3.0, 4.0, 5.0)
+ return beam.AddFixedKey(s, vals)
+ },
+ count: 5,
+ },
+ }
+
+ for _, test := range tests {
+ test := test
+ t.Run(fmt.Sprintf("_%v", test.name), func(t *testing.T) {
+ p := beam.NewPipeline()
+ s := p.Root()
+ in := test.in(s)
+ exp := beam.Create(s, test.count)
+ count := CountElms(s, in)
+ passert.Equals(s, count, exp)
+
+ if err := ptest.Run(p); err != nil {
+ t.Errorf("CountElms != %v: %v", test.count, err)
+ }
+ })
+ }
+}

sdks/go/pkg/beam/transforms/stats/util_gen.go

@@ -22,4 +22,4 @@ package stats
 // `go generate` executes go:generate commands in lexical file order, top to bottom.
 
 //go:generate go install github.com/apache/beam/sdks/go/cmd/starcgen
-//go:generate starcgen --package=stats --identifiers=mapFn,meanFn,maxIntFn,minIntFn,sumIntFn,maxInt8Fn,minInt8Fn,sumInt8Fn,maxInt16Fn,minInt16Fn,sumInt16Fn,maxInt32Fn,minInt32Fn,sumInt32Fn,maxInt64Fn,minInt64Fn,sumInt64Fn,maxUintFn,minUintFn,sumUintFn,maxUint8Fn,minUint8Fn,sumUint8Fn,maxUint16Fn,minUint16Fn,sumUint16Fn,maxUint32Fn,minUint32Fn,sumUint32Fn,maxUint64Fn,minUint64Fn,sumUint64Fn,maxFloat32Fn,minFloat32Fn,sumFloat32Fn,maxFloat64Fn,minFloat64Fn,sumFloat64Fn
+//go:generate starcgen --package=stats --identifiers=countFn,keyedCountFn,meanFn,maxIntFn,minIntFn,sumIntFn,maxInt8Fn,minInt8Fn,sumInt8Fn,maxInt16Fn,minInt16Fn,sumInt16Fn,maxInt32Fn,minInt32Fn,sumInt32Fn,maxInt64Fn,minInt64Fn,sumInt64Fn,maxUintFn,minUintFn,sumUintFn,maxUint8Fn,minUint8Fn,sumUint8Fn,maxUint16Fn,minUint16Fn,sumUint16Fn,maxUint32Fn,minUint32Fn,sumUint32Fn,maxUint64Fn,minUint64Fn,sumUint64Fn,maxFloat32Fn,minFloat32Fn,sumFloat32Fn,maxFloat64Fn,minFloat64Fn,sumFloat64Fn

sdks/go/pkg/beam/transforms/stats/util_gen.tmpl

@@ -21,6 +21,6 @@ package stats
 
 //go:generate go install github.com/apache/beam/sdks/go/cmd/starcgen
 {{- with $x := .X }}
-//go:generate starcgen --package=stats --identifiers=mapFn,meanFn{{- range $i, $t := $x -}},max{{$t.Name}}Fn,min{{$t.Name}}Fn,sum{{$t.Name}}Fn{{- end -}}
+//go:generate starcgen --package=stats --identifiers=countFn,keyedCountFn,meanFn{{- range $i, $t := $x -}},max{{$t.Name}}Fn,min{{$t.Name}}Fn,sum{{$t.Name}}Fn{{- end -}}
 {{end}}