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ARROW-13067: [C++][Compute] Implement integer to decimal cast #11045

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ARROW-13067: [C++][Compute] Implement integer to decimal cast #11045

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ARROW-13067: [C++][Compute] Implement integer to decimal cast
cyb70289 Aug 31, 2021
186d356
refine error message of insufficient precision
cyb70289 Sep 2, 2021
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14 changes: 12 additions & 2 deletions cpp/src/arrow/compute/kernels/scalar_arithmetic_test.cc
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Expand Up @@ -1365,6 +1365,18 @@ TEST(TestBinaryDecimalArithmetic, DispatchBest) {
}
}

// decimal, integer
for (std::string name : {"add", "subtract", "multiply", "divide"}) {
for (std::string suffix : {"", "_checked"}) {
name += suffix;

CheckDispatchBest(name, {int64(), decimal128(1, 0)},
{decimal128(1, 0), decimal128(1, 0)});
CheckDispatchBest(name, {decimal128(1, 0), int64()},
{decimal128(1, 0), decimal128(1, 0)});
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@pitrou pitrou Sep 1, 2021

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Hmm, so an int64 is cast to a 1-digit decimal? Unrelated to this PR surely, but I'm a bit surprised :-)

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@lidavidm lidavidm Sep 1, 2021

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I think this is testing that given an integer and a decimal, the integer is cast to a decimal of the same width/precision/scale.

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@pitrou pitrou Sep 1, 2021

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But surely the actual cast from int64 to decimal128(1,0) will fail in the precision check?

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@lidavidm lidavidm Sep 1, 2021

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Ah, right. Maybe we want the cast logic to be smarter about that, then. As you said, though, that can be tackled separately.

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@cyb70289 cyb70289 Sep 2, 2021

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Jira issue created
https://issues.apache.org/jira/browse/ARROW-13856

}
}

// decimal, decimal
for (std::string name : {"add", "subtract"}) {
for (std::string suffix : {"", "_checked"}) {
Expand Down Expand Up @@ -1410,8 +1422,6 @@ TEST(TestBinaryDecimalArithmetic, DispatchBest) {
{decimal256(6, 4), decimal256(6, 4)});
}
}

// TODO(ARROW-13067): add 'integer, decimal' tests
}

// reference result from bc (precsion=100, scale=40)
Expand Down
59 changes: 59 additions & 0 deletions cpp/src/arrow/compute/kernels/scalar_cast_numeric.cc
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Expand Up @@ -391,6 +391,53 @@ struct CastFunctor<O, I,
}
};

// ----------------------------------------------------------------------
// Integer to decimal

struct IntegerToDecimal {
template <typename OutValue, typename IntegerType>
OutValue Call(KernelContext*, IntegerType val, Status* st) const {
auto maybe_decimal = OutValue(val).Rescale(0, out_scale_);
if (ARROW_PREDICT_TRUE(maybe_decimal.ok())) {
return maybe_decimal.MoveValueUnsafe();
}
*st = maybe_decimal.status();
return OutValue{};
}

int32_t out_scale_;
};

template <typename O, typename I>
struct CastFunctor<O, I,
enable_if_t<is_decimal_type<O>::value && is_integer_type<I>::value>> {
static Status Exec(KernelContext* ctx, const ExecBatch& batch, Datum* out) {
const auto& out_type = checked_cast<const O&>(*out->type());
const auto out_scale = out_type.scale();
const auto out_precision = out_type.precision();

// verify precision and scale
if (out_scale < 0) {
return Status::Invalid("Scale must be non-negative");
}
// maximal number of decimal digits for int8/16/32/64
constexpr std::array<int, 4> decimal_digits{3, 5, 10, 19};
using ctype = typename I::c_type;
static_assert(sizeof(ctype) <= 8, "");
const int precision = decimal_digits[BitUtil::Log2(sizeof(ctype))] + out_scale;
if (out_precision < precision) {
return Status::Invalid(
"Precision is not great enough for the result. "
"It should be at least ",
precision);
}

applicator::ScalarUnaryNotNullStateful<O, I, IntegerToDecimal> kernel(
IntegerToDecimal{out_scale});
return kernel.Exec(ctx, batch, out);
}
};

// ----------------------------------------------------------------------
// Decimal to decimal

Expand Down Expand Up @@ -641,6 +688,12 @@ std::shared_ptr<CastFunction> GetCastToDecimal128() {
DCHECK_OK(func->AddKernel(Type::DOUBLE, {float64()}, sig_out_ty,
CastFunctor<Decimal128Type, DoubleType>::Exec));

// Cast from integer
for (const std::shared_ptr<DataType>& in_ty : IntTypes()) {
auto exec = GenerateInteger<CastFunctor, Decimal128Type>(in_ty->id());
DCHECK_OK(func->AddKernel(in_ty->id(), {in_ty}, sig_out_ty, std::move(exec)));
}

// Cast from other decimal
auto exec = CastFunctor<Decimal128Type, Decimal128Type>::Exec;
// We resolve the output type of this kernel from the CastOptions
Expand All @@ -664,6 +717,12 @@ std::shared_ptr<CastFunction> GetCastToDecimal256() {
DCHECK_OK(func->AddKernel(Type::DOUBLE, {float64()}, sig_out_ty,
CastFunctor<Decimal256Type, DoubleType>::Exec));

// Cast from integer
for (const std::shared_ptr<DataType>& in_ty : IntTypes()) {
auto exec = GenerateInteger<CastFunctor, Decimal256Type>(in_ty->id());
DCHECK_OK(func->AddKernel(in_ty->id(), {in_ty}, sig_out_ty, std::move(exec)));
}

// Cast from other decimal
auto exec = CastFunctor<Decimal256Type, Decimal128Type>::Exec;
DCHECK_OK(
Expand Down
34 changes: 33 additions & 1 deletion cpp/src/arrow/compute/kernels/scalar_cast_test.cc
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Expand Up @@ -71,9 +71,11 @@ static std::vector<std::shared_ptr<DataType>> kNumericTypes = {
uint8(), int8(), uint16(), int16(), uint32(),
int32(), uint64(), int64(), float32(), float64()};

static std::vector<std::shared_ptr<DataType>> kDictionaryIndexTypes = {
static std::vector<std::shared_ptr<DataType>> kIntegerTypes = {
int8(), uint8(), int16(), uint16(), int32(), uint32(), int64(), uint64()};

static std::vector<std::shared_ptr<DataType>> kDictionaryIndexTypes = kIntegerTypes;

static std::vector<std::shared_ptr<DataType>> kBaseBinaryTypes = {
binary(), utf8(), large_binary(), large_utf8()};

Expand Down Expand Up @@ -587,6 +589,36 @@ TEST(Cast, Decimal256ToInt) {
CheckCast(negative_scale, ArrayFromJSON(int64(), "[1234567890000, -120000]"), options);
}

TEST(Cast, IntegerToDecimal) {
for (auto decimal_type : {decimal128(21, 2), decimal256(21, 2)}) {
for (auto integer_type : kIntegerTypes) {
CheckCast(
ArrayFromJSON(integer_type, "[0, 7, null, 100, 99]"),
ArrayFromJSON(decimal_type, R"(["0.00", "7.00", null, "100.00", "99.00"])"));
}
}

// extreme value
for (auto decimal_type : {decimal128(19, 0), decimal256(19, 0)}) {
CheckCast(ArrayFromJSON(int64(), "[-9223372036854775808, 9223372036854775807]"),
ArrayFromJSON(decimal_type,
R"(["-9223372036854775808", "9223372036854775807"])"));
CheckCast(ArrayFromJSON(uint64(), "[0, 18446744073709551615]"),
ArrayFromJSON(decimal_type, R"(["0", "18446744073709551615"])"));
}

// insufficient output precision
{
CastOptions options;

options.to_type = decimal128(5, 3);
CheckCastFails(ArrayFromJSON(int8(), "[0]"), options);

options.to_type = decimal256(76, 67);
CheckCastFails(ArrayFromJSON(int32(), "[0]"), options);
}
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@lidavidm lidavidm Sep 1, 2021

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Should we file a follow up issue to allow truncation via an unsafe cast in these cases?

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@cyb70289 cyb70289 Sep 2, 2021

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Sure, will do.

}

TEST(Cast, Decimal128ToDecimal128) {
CastOptions options;

Expand Down