IPC reads do not return mutable buffers right now, so Buffer::mutable_data will return nullptr. You need to use Buffer::Copy
https://github.com/apache/arrow/blob/master/cpp/src/arrow/buffer.h#L251 You could potentially use const_cast to get a mutable pointer to a buffer returned by IPC reads, which are always immutable buffers — we could potentially add a flag to IpcReadOptions to permit returning mutable buffers. On Fri, Jul 30, 2021 at 12:49 PM Niranda Perera <niranda.per...@gmail.com> wrote: > > Hi Rares, > > ArrayData::GetMutableValues would return a nullptr if the requested buffer > is not available. > https://github.com/apache/arrow/blob/557a7c63d49aa04508564517c77c71f3657d19ff/cpp/src/arrow/array/data.h#L199 > > What does nAtts stand for? could it be that it is OOB? > > On Fri, Jul 30, 2021 at 12:55 PM Rares Vernica <rvern...@gmail.com> wrote: > > > Hello, > > > > I have a RecordBatch that I read from an IPC file. I need to run a > > cumulative sum on one of the int64 arrays in the batch. I tried to do: > > > > std::shared_ptr<arrow::ArrayData> pos_data = batch->column_data(nAtts); > > auto pos_values = pos_data->GetMutableValues<int64_t>(1); > > for (auto i = 1; i < pos_data->length; i++) > > pos_values[i] += pos_values[i - 1]; > > > > but GetMutableValues returns NULL. If I use GetValue, it works fine, but I > > can't run the cumulative sum on the returned pointer since it is read-only. > > I tried creating a copy of ArryaData like so: > > > > std::shared_ptr<arrow::ArrayData> pos_data = > > batch->column_data(nAtts)->Copy(); > > > > but it did not help. All this data is in CPU buffers so I'm not sure what > > is the problem. What is the best way to mutate or copy & mutate it? > > > > Thanks! > > Rares > > > > > -- > Niranda Perera > https://niranda.dev/ > @n1r44 <https://twitter.com/N1R44>
