pitrou commented on a change in pull request #8269:
URL: https://github.com/apache/arrow/pull/8269#discussion_r496686115
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File path: cpp/src/arrow/compute/kernels/aggregate_test.cc
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@@ -914,5 +914,127 @@ TEST_F(TestInt32ModeKernel, LargeValueRange) {
CheckModeWithRange<ArrowType>(-10000000, 10000000);
}
+//
+// Var/Std
+//
+
+template <typename ArrowType>
+class TestPrimitiveVarStdKernel : public ::testing::Test {
+ public:
+ using Traits = TypeTraits<ArrowType>;
+ using ScalarType = typename TypeTraits<DoubleType>::ScalarType;
+
+ void AssertVarStdIs(const Datum& array, const VarStdOptions& options,
+ double expected_var, double diff = 0) {
+ ASSERT_OK_AND_ASSIGN(Datum out_var, Var(array, options));
+ ASSERT_OK_AND_ASSIGN(Datum out_std, Std(array, options));
+ auto var = checked_cast<const ScalarType*>(out_var.scalar().get());
+ auto std = checked_cast<const ScalarType*>(out_std.scalar().get());
+ ASSERT_TRUE(var->is_valid && std->is_valid);
+ ASSERT_DOUBLE_EQ(std->value * std->value, var->value);
+ if (diff == 0) {
+ ASSERT_DOUBLE_EQ(var->value, expected_var); // < 4ULP
+ } else {
+ ASSERT_NEAR(var->value, expected_var, diff);
+ }
+ }
+
+ void AssertVarStdIs(const std::string& json, const VarStdOptions& options,
+ double expected_var) {
+ auto array = ArrayFromJSON(type_singleton(), json);
+ AssertVarStdIs(array, options, expected_var);
+ }
+
+ void AssertVarStdIs(const std::vector<std::string>& json, const
VarStdOptions& options,
+ double expected_var) {
+ auto chunked = ChunkedArrayFromJSON(type_singleton(), json);
+ AssertVarStdIs(chunked, options, expected_var);
+ }
+
+ void AssertVarStdIsInvalid(const Datum& array, const VarStdOptions& options)
{
+ ASSERT_OK_AND_ASSIGN(Datum out_var, Var(array, options));
+ ASSERT_OK_AND_ASSIGN(Datum out_std, Std(array, options));
+ auto var = checked_cast<const ScalarType*>(out_var.scalar().get());
+ auto std = checked_cast<const ScalarType*>(out_std.scalar().get());
+ ASSERT_FALSE(var->is_valid || std->is_valid);
+ }
+
+ void AssertVarStdIsInvalid(const std::string& json, const VarStdOptions&
options) {
+ auto array = ArrayFromJSON(type_singleton(), json);
+ AssertVarStdIsInvalid(array, options);
+ }
+
+ std::shared_ptr<DataType> type_singleton() { return
Traits::type_singleton(); }
+};
+
+template <typename ArrowType>
+class TestNumericVarStdKernel : public TestPrimitiveVarStdKernel<ArrowType> {};
+
+// Reference value from numpy.var
+TYPED_TEST_SUITE(TestNumericVarStdKernel, NumericArrowTypes);
+TYPED_TEST(TestNumericVarStdKernel, Basics) {
+ VarStdOptions options; // ddof = 0, population var/std
+
+ this->AssertVarStdIs("[100]", options, 0);
+ this->AssertVarStdIs("[1, 2, 3]", options, 0.6666666666666666);
+ this->AssertVarStdIs("[null, 1, 2, null, 3]", options, 0.6666666666666666);
+
+ this->AssertVarStdIs({"[]", "[1]", "[2]", "[null]", "[3]"}, options,
+ 0.6666666666666666);
+ this->AssertVarStdIs({"[1, 2, 3]", "[4, 5, 6]", "[7, 8]"}, options, 5.25);
Review comment:
Can we also test with chunks of very different sizes? For example `[1,
2, 3, 4, 5, 6, 7]` and `[8]`.
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