vibhatha commented on code in PR #13397:
URL: https://github.com/apache/arrow/pull/13397#discussion_r901754257
##########
r/src/compute.cpp:
##########
@@ -574,3 +576,90 @@ SEXP compute__CallFunction(std::string func_name,
cpp11::list args, cpp11::list
std::vector<std::string> compute__GetFunctionNames() {
return arrow::compute::GetFunctionRegistry()->GetFunctionNames();
}
+
+class RScalarUDFCallable : public arrow::compute::ArrayKernelExec {
+ public:
+ RScalarUDFCallable(const std::shared_ptr<arrow::Schema>& input_types,
+ const std::shared_ptr<arrow::DataType>& output_type,
cpp11::sexp fun)
+ : input_types_(input_types), output_type_(output_type), fun_(fun) {}
+
+ arrow::Status operator()(arrow::compute::KernelContext* context,
+ const arrow::compute::ExecSpan& span,
+ arrow::compute::ExecResult* result) {
+ std::vector<std::shared_ptr<arrow::Array>> array_args;
+ for (int64_t i = 0; i < span.num_values(); i++) {
+ const arrow::compute::ExecValue& v = span[i];
+ if (v.is_array()) {
+ array_args.push_back(v.array.ToArray());
+ } else if (v.is_scalar()) {
+ auto array = ValueOrStop(arrow::MakeArrayFromScalar(*v.scalar,
span.length));
+ array_args.push_back(array);
+ }
+ }
+
+ auto batch = arrow::RecordBatch::Make(input_types_, span.length,
array_args);
+
+ auto fun_result = SafeCallIntoR<std::shared_ptr<arrow::Array>>([&]() {
+ cpp11::sexp batch_sexp = cpp11::to_r6<arrow::RecordBatch>(batch);
+ cpp11::sexp batch_length_sexp = cpp11::as_sexp(span.length);
+
+ cpp11::writable::list udf_context = {batch_length_sexp};
+ udf_context.names() = {"batch_length"};
+
+ cpp11::sexp fun_result_sexp = fun_(udf_context, batch_sexp);
+ if (!Rf_inherits(fun_result_sexp, "Array")) {
+ cpp11::stop("arrow_scalar_function must return an Array");
+ }
+
+ return cpp11::as_cpp<std::shared_ptr<arrow::Array>>(fun_result_sexp);
+ });
+
+ if (!fun_result.ok()) {
+ return fun_result.status();
+ }
+
+ result->value.emplace<std::shared_ptr<arrow::ArrayData>>(
+ fun_result.ValueUnsafe()->data());
+ return arrow::Status::OK();
+ }
+
+ private:
+ std::shared_ptr<arrow::Schema> input_types_;
+ std::shared_ptr<arrow::DataType> output_type_;
+ cpp11::function fun_;
+};
+
+// [[arrow::export]]
+void RegisterScalarUDF(std::string name, cpp11::sexp fun) {
+ const arrow::compute::FunctionDoc dummy_function_doc{
+ "A user-defined R function", "returns something", {"..."}};
+
+ auto func = std::make_shared<arrow::compute::ScalarFunction>(
+ name, arrow::compute::Arity::VarArgs(), dummy_function_doc);
Review Comment:
In my understanding, the function docs are used at the function registration
step. I am not quite sure if the query engine cares much about it. It would be
the compute API which is the interested party. For example this is how it is
used in [Python
UDFs](https://github.com/apache/arrow/blob/207d328565b65b2c916ec17bc57f29b0c6fc8e8f/python/pyarrow/tests/test_udf.py#L44).
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