Implement RecordBatchFileReader::readRecordBatchAtIndex(...)

matlab/src/cpp/arrow/matlab/error/error.h

@@ -244,5 +244,7 @@ static const char* C_EXPORT_FAILED = "arrow:c:export:ExportFailed";
 static const char* C_IMPORT_FAILED = "arrow:c:import:ImportFailed";
 static const char* IPC_RECORD_BATCH_WRITE_FAILED = "arrow:io:ipc:FailedToWriteRecordBatch";
 static const char* IPC_RECORD_BATCH_READER_OPEN_FAILED = "arrow:io:ipc:FailedToOpenRecordBatchReader";
+static const char* IPC_RECORD_BATCH_READ_INVALID_INDEX = "arrow:io:ipc:InvalidIndex";
+static const char* IPC_RECORD_BATCH_READ_FAILED = "arrow:io:ipc:ReadFailed";
 
 }  // namespace arrow::matlab::error

matlab/src/cpp/arrow/matlab/io/ipc/proxy/record_batch_file_reader.cc

@@ -18,18 +18,31 @@
 #include "arrow/io/file.h"
 #include "arrow/matlab/error/error.h"
 #include "arrow/matlab/io/ipc/proxy/record_batch_file_reader.h"
+#include "arrow/matlab/tabular/proxy/record_batch.h"
 #include "arrow/matlab/tabular/proxy/schema.h"
 #include "arrow/util/utf8.h"
 
 #include "libmexclass/proxy/ProxyManager.h"
 
 namespace arrow::matlab::io::ipc::proxy {
 
+namespace {
+  libmexclass::error::Error makeInvalidNumericIndexError(const int32_t matlab_index,
+                                                        const int32_t num_batches) {
+    std::stringstream error_message_stream;
+    error_message_stream << "Invalid record batch index: ";
+    error_message_stream << matlab_index;
+    error_message_stream << ". Record batch index must be between 1 and the number of record batches (";
+    error_message_stream << num_batches;
+    error_message_stream << ").";
+    return libmexclass::error::Error{error::IPC_RECORD_BATCH_READ_INVALID_INDEX, error_message_stream.str()};
+  }
+}
+
 RecordBatchFileReader::RecordBatchFileReader(const std::shared_ptr<arrow::ipc::RecordBatchFileReader> reader)
   : reader{std::move(reader)} {
     REGISTER_METHOD(RecordBatchFileReader, getNumRecordBatches);
     REGISTER_METHOD(RecordBatchFileReader, getSchema);
-
   }
 
 libmexclass::proxy::MakeResult RecordBatchFileReader::make(const libmexclass::proxy::FunctionArguments& constructor_arguments) {
@@ -75,9 +88,33 @@ void RecordBatchFileReader::getSchema(libmexclass::proxy::method::Context& conte
   mda::ArrayFactory factory;
   const auto schema_proxy_id_mda = factory.createScalar(schema_proxy_id);
   context.outputs[0] = schema_proxy_id_mda;
-
 }
 
+void RecordBatchFileReader::readRecordBatchAtIndex(libmexclass::proxy::method::Context& context) {
+  namespace mda = ::matlab::data;
+  using RecordBatchProxy = arrow::matlab::tabular::proxy::RecordBatch;
+
+  mda::StructArray opts = context.inputs[0];
+  const mda::TypedArray<int32_t> matlab_index_mda = opts[0]["Index"];
+
+  const auto matlab_index = matlab_index_mda[0];
+  const auto num_record_batches = reader->num_record_batches();
+  if (matlab_index < 1 || matlab_index > num_record_batches) {
+    context.error = makeInvalidNumericIndexError(matlab_index, num_record_batches);
+    return;
+  }
+  const auto arrow_index = matlab_index - 1;
+
+  MATLAB_ASSIGN_OR_ERROR_WITH_CONTEXT(const auto record_batch, reader->ReadRecordBatch(arrow_index),
+                                       context, error::IPC_RECORD_BATCH_READ_FAILED);
+
+  auto record_batch_proxy = std::make_shared<RecordBatchProxy>(std::move(record_batch));
+  const auto record_batch_proxy_id = libmexclass::proxy::ProxyManager::manageProxy(record_batch_proxy);
+
+  mda::ArrayFactory factory;
+  const auto record_batch_proxyy_id_mda = factory.createScalar(record_batch_proxy_id);
+  context.outputs[0] = record_batch_proxyy_id_mda;
+}
 
 
 

matlab/src/cpp/arrow/matlab/io/ipc/proxy/record_batch_file_reader.h

@@ -37,6 +37,9 @@ class RecordBatchFileReader : public libmexclass::proxy::Proxy {
 
     void getSchema(libmexclass::proxy::method::Context& context);
 
+    void readRecordBatchAtIndex(libmexclass::proxy::method::Context& context);
+
+
 
 };