On Fri, 30 Jul 2021 18:55:33 +0200 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:
The ArrayData contents are semantically immutable. You may want to grab mutable pointers to the underlying data, but you're generally on your own. > 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(); ArrayData::Copy() creates a shallow copy of the ArrayData structure. We do not include a deep copy facility, because often you only want to change one of the underlying buffers. > 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? You should probably recreate a new ArrayData with the desired buffers. To create a buffer, there are several possibilities: allocate it directly (using AllocateBuffer, for example), use TypedBufferBuilder<T>, or a hand-rolled method of your choice. Regards Antoine.
