Hi Wes, Thanks for the reply, but I don't think this is what I am looking for.
It seems to me this `result.to_array()` will only return the array for the selection vector ( https://github.com/apache/arrow/blob/b07c2626cb3cdd3498b41da9feedf7c8319baa27/python/pyarrow/gandiva.pyx#L130), but it is not clear to me how I can use the selection vector to filter the original record batch. If I understand correctly, in this test case, `result.to_array().equals(pa. array(range(1000), type=pa.uint32()))` is asserting that the selection vector has integer index values from [0, 1000), but I am looking for to obtain an array in the filtered record batch which should be an array of floats here. I know I can iterate indices in the selection vector and use it to retrieve each row in original record batch columns, but I am not certain if this is the right way to do it. For example, if I have multiple columns in the original record batch, do I need to iterate the selection vector multiple times to filter each of the column? Since this is a common task, I expect there is an easy/efficient API to do this. Basically, I am looking for something like: selection_vector = filter.evaluate(record_batch, pa.default_memory_pool()) filtered_column_arrays_in_record_batch = record_batch.filter(selection_vector) # what is the API for doing this? In the C++ test cases, the closest thing I find is to construct a gandiva projector to use the selection vector, but every test case there requires client to construct a gandiva expression to build the projector (for example, in this test case, a {sum_expr} is used for constructing the projector, https://github.com/apache/arrow/blob/967728fe4654e5d53bc0789e64e5a9ba7f27f263/cpp/src/gandiva/tests/filter_project_test.cc#L121 ). I wonder if the filtering can be done without involving creating a projection expression. At the same time, if projector is expected to be used for doing this, what projector expressions should be used if I want to keep all the columns as they are but just with some rows filtered based on the criteria given? On Sun, Apr 5, 2020 at 7:27 AM Wes McKinney <[email protected]> wrote: > You can see an example of filtering via the Python bindings > > > https://github.com/apache/arrow/blob/master/python/pyarrow/tests/test_gandiva.py#L89 > > This creates a gandiva::Filter using gandiva::Filter::Make, which can > be used to filter a RecordBatch > > Is this what you need? > > On Fri, Apr 3, 2020 at 7:12 PM Yue Ni <[email protected]> wrote: > > > > Hi there, > > > > I am using the gandiva C++ library for processing RecordBatch. I would > like to know how I can apply gandiva::Filter for a RecordBatch so that I > can do some filtering without using the projector. > > > > Since I don't find any documentation for it, I read some source code > about its usage, and here are the test cases I found about its usage: > > 1) > https://github.com/apache/arrow/blob/967728fe4654e5d53bc0789e64e5a9ba7f27f263/cpp/src/gandiva/tests/filter_test.cc > > 2) > https://github.com/apache/arrow/blob/967728fe4654e5d53bc0789e64e5a9ba7f27f263/cpp/src/gandiva/tests/filter_project_test.cc > > > > From my reading, I find it is possible to get a SelectionVector by using > the gandiva::Filter, at the same time, you can use the SelectionVector with > the gandiva::Projector to filter RecordBatch when doing projection. My > questions are: > > 1) if I don't want to do any projection but simply filtering, what is > the recommended way to do it? > > 2) I am trying to handle the case like "SELECT * FROM table WHERE blah", > is it recommended to apply filtering without projection in this case or is > there any alternative approach doing it? > > > > Thanks. > > > > Regards, > > Yue > > >
