vibhatha commented on code in PR #13397:
URL: https://github.com/apache/arrow/pull/13397#discussion_r901703174
##########
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:
@paleolimbot I am not quite sure about extracting the function doc in R as
well. I was merely referring to a string passed as the function docs explicitly
if required. In Python I was looking into the `inspect` API and it can help
with this. For Python UDFs, I did a little bit of a check if we can use it to
extract all the required values to register a UDF. It seems possible. I was
just curious how it is planned to handle such things in R API.
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