[GitHub] [arrow] lidavidm commented on a diff in pull request #13974: ARROW-17527: [Go] Implement Cast to Boolean Functions

[GitBox <gi...@apache.org>]

lidavidm commented on code in PR #13974:
URL: https://github.com/apache/arrow/pull/13974#discussion_r956151661


##########
go/arrow/compute/cast_test.go:
##########
@@ -0,0 +1,329 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package compute_test
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/apache/arrow/go/v10/arrow"
+	"github.com/apache/arrow/go/v10/arrow/array"
+	"github.com/apache/arrow/go/v10/arrow/compute"
+	"github.com/apache/arrow/go/v10/arrow/memory"
+	"github.com/apache/arrow/go/v10/arrow/scalar"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/stretchr/testify/suite"
+)
+
+func getScalars(inputs []compute.Datum, idx int) []scalar.Scalar {
+	out := make([]scalar.Scalar, len(inputs))
+	for i, in := range inputs {
+		if in.Kind() == compute.KindArray {
+			arr := in.(*compute.ArrayDatum).MakeArray()
+			defer arr.Release()
+			out[i], _ = scalar.GetScalar(arr, idx)
+		} else {
+			out[i] = in.(*compute.ScalarDatum).Value
+		}
+	}
+	return out
+}
+
+func getDatums[T any](inputs []T) []compute.Datum {
+	out := make([]compute.Datum, len(inputs))
+	for i, in := range inputs {
+		out[i] = compute.NewDatum(in)
+	}
+	return out
+}
+
+func assertDatumsEqual(t *testing.T, expected, actual compute.Datum) {
+	require.Equal(t, expected.Kind(), actual.Kind())
+
+	switch expected.Kind() {
+	case compute.KindScalar:
+		want := expected.(*compute.ScalarDatum).Value
+		got := actual.(*compute.ScalarDatum).Value

Review Comment:
   I guess we'd just eat a panic if the actual value wasn't the right Kind? Is it worth doing an explicit check or is the regular message clear enough?



##########
go/arrow/compute/internal/kernels/cast.go:
##########
@@ -0,0 +1,120 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package kernels
+
+import (
+	"github.com/apache/arrow/go/v10/arrow"
+	"github.com/apache/arrow/go/v10/arrow/array"
+	"github.com/apache/arrow/go/v10/arrow/compute/internal/exec"
+)
+
+type CastOptions struct {
+	ToType               arrow.DataType `compute:"to_type"`
+	AllowIntOverflow     bool           `compute:"allow_int_overflow"`
+	AllowTimeTruncate    bool           `compute:"allow_time_truncate"`
+	AllowTimeOverflow    bool           `compute:"allow_time_overflow"`
+	AllowDecimalTruncate bool           `compute:"allow_decimal_truncate"`
+	AllowFloatTruncate   bool           `compute:"allow_float_truncate"`
+	AllowInvalidUtf8     bool           `compute:"allow_invalid_utf8"`
+}
+
+func (CastOptions) TypeName() string { return "CastOptions" }
+
+// CastState is the kernel state for Cast functions, it is an alias to
+// the CastOptions object.
+type CastState = CastOptions
+
+// ZeroCopyCastExec is a kernel for performing a cast which can be executed
+// as a zero-copy operation. It simply forwards the buffers to the output.
+//
+// This can be used for casting a type to itself, or for casts between
+// equivalent representations such as Int32 and Date32.
+func ZeroCopyCastExec(_ *exec.KernelCtx, batch *exec.ExecSpan, out *exec.ExecResult) error {
+	dt := out.Type
+	*out = batch.Values[0].Array
+	out.Type = dt
+	return nil
+}
+
+func recursiveSetSelfAlloc(arr *exec.ArraySpan) {
+	for i := range arr.Buffers {
+		if len(arr.Buffers[i].Buf) > 0 {
+			arr.Buffers[i].SelfAlloc = true
+			if arr.Buffers[i].Owner != nil {
+				arr.Buffers[i].Owner.Retain()
+			}
+		}
+	}
+
+	for i := range arr.Children {
+		recursiveSetSelfAlloc(&arr.Children[i])
+	}
+}
+
+// CastFromNull is a simple kernel for constructing an array of null values
+// for the requested data type, allowing casting of an arrow.Null typed value
+// to any other arbitrary data type.
+func CastFromNull(ctx *exec.KernelCtx, batch *exec.ExecSpan, out *exec.ExecResult) error {
+	arr := array.MakeArrayOfNull(exec.GetAllocator(ctx.Ctx), out.Type, int(batch.Len))
+	defer arr.Release()
+
+	out.SetMembers(arr.Data())
+	recursiveSetSelfAlloc(out)
+	return nil
+}
+
+// OutputAllNull is a simple kernel that initializes the output as an array
+// whose output is all null by setting nulls to the length.
+func OutputAllNull(_ *exec.KernelCtx, batch *exec.ExecSpan, out *exec.ExecResult) error {
+	out.Nulls = batch.Len
+	return nil
+}
+
+func canCastFromDict(id arrow.Type) bool {
+	return arrow.IsPrimitive(id) || arrow.IsBaseBinary(id) || arrow.IsFixedSizeBinary(id)
+}
+
+// GetZeroCastKernel returns a kernel for performing ZeroCast execution using
+// the ZeroCopyCastExec kernel function.
+func GetZeroCastKernel(inID arrow.Type, inType exec.InputType, out exec.OutputType) exec.ScalarKernel {
+	k := exec.NewScalarKernel([]exec.InputType{inType}, out, ZeroCopyCastExec, nil)
+	k.NullHandling = exec.NullComputedNoPrealloc
+	k.MemAlloc = exec.MemNoPrealloc
+	return k
+}
+
+// GetCommonCastKernels returns the list of kernels common to all types
+// such as casting from null or from Extension types of the appropriate
+// underlying type.
+func GetCommonCastKernels(outID arrow.Type, outType arrow.DataType) (out []exec.ScalarKernel) {
+	out = make([]exec.ScalarKernel, 0, 2)
+
+	kernel := exec.NewScalarKernel([]exec.InputType{exec.NewExactInput(arrow.Null)}, exec.NewOutputType(outType),
+		CastFromNull, nil)
+	kernel.NullHandling = exec.NullComputedNoPrealloc
+	kernel.MemAlloc = exec.MemNoPrealloc
+	out = append(out, kernel)
+
+	// if canCastFromDict(outID) {
+	// dictionary unpacking not implemented for boolean or nested types
+	// TODO dict cast
+	// panic(fmt.Errorf("%w: dictionary casting", arrow.ErrNotImplemented))
+	// }
+
+	// Cast from extension
+	return

Review Comment:
   Just remove the commented out code/comments that don't apply?



##########
go/arrow/compute/internal/kernels/helpers.go:
##########
@@ -0,0 +1,119 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package kernels
+
+import (
+	"github.com/apache/arrow/go/v10/arrow/bitutil"
+	"github.com/apache/arrow/go/v10/arrow/compute/internal/exec"
+	"github.com/apache/arrow/go/v10/internal/bitutils"
+)
+
+// ScalarUnary returns a kernel for performing a unary operation on
+// FixedWidth types which is implemented using the passed in function
+// which will receive a slice containing the raw input data along with
+// a slice to populate for the output data.
+//
+// Note that bool is not included in exec.FixedWidthTypes since it is
+// represented as a bitmap, not as a slice of bool.
+func ScalarUnary[OutT, Arg0T exec.FixedWidthTypes](op func(*exec.KernelCtx, []Arg0T, []OutT) error) exec.ArrayKernelExec {
+	return func(ctx *exec.KernelCtx, in *exec.ExecSpan, out *exec.ExecResult) error {
+		arg0 := in.Values[0].Array
+		inData := exec.GetSpanValues[Arg0T](&arg0, 1)
+		outData := exec.GetSpanValues[OutT](out, 1)
+		return op(ctx, inData, outData)
+	}
+}
+
+// ScalarUnaryBoolOutput is like ScalarUnary only it is for cases of boolean
+// output. The function should take in a slice of the input type and a slice
+// of bytes to fill with the output boolean bitmap.
+func ScalarUnaryBoolOutput[Arg0T exec.FixedWidthTypes](op func(*exec.KernelCtx, []Arg0T, []byte) error) exec.ArrayKernelExec {
+	return func(ctx *exec.KernelCtx, in *exec.ExecSpan, out *exec.ExecResult) error {
+		arg0 := in.Values[0].Array
+		inData := exec.GetSpanValues[Arg0T](&arg0, 1)
+		return op(ctx, inData, out.Buffers[1].Buf)
+	}
+}
+
+// ScalarUnaryNotNullBinaryArgBoolOut creates a unary kernel that accepts
+// a binary type input (Binary [offset int32], String [offset int32],
+// LargeBinary [offset int64], LargeString [offset int64]) and returns
+// a boolean output which is never null.
+//
+// It implements the handling to iterate the offsets and values calling
+// the provided function on each byte slice. The provided default value
+// will be used as the output for elements of the input that are null.
+func ScalarUnaryNotNullBinaryArgBoolOut[OffsetT int32 | int64](defVal bool, op func(*exec.KernelCtx, []byte) (bool, error)) exec.ArrayKernelExec {

Review Comment:
   just a general comment, but seeing as these are patterned after the C++ names, the C++ names aren't very consistent/don't follow a consistent convention - you may want to consider something more principled. (I think @edponce was trying to refactor them a while back, but it's a lot of work)



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