hi Wenjian -- I am not an expert in the Java library. Perhaps Bryan, Li, Jacques, or Sidd can point you in the right direction. You can take a look at the Dremio codebase to see more examples of Arrow in action
https://github.com/dremio/dremio-oss - Wes On Tue, Aug 14, 2018 at 10:08 PM, Xu,Wenjian <[email protected]> wrote: > Hi Wes, > > Thank you for your kind help. > > Actually I am working on the Java UDF iterating the *array<string>* in SQL > language. > > I understand that , in order to represent *array<string>* in Arrow format, I > could use ListVector with VarCharVector as the inner list. My question is, > how to efficiently access the all the elements (i.e., each byte[] as > string)? > > By checking the test code: > https://github.com/apache/arrow/blob/master/java/vector/src/test/java/org/apache/arrow/vector/TestListVector.java > > one option is to use ListVector.getObject(int index) to get each > ArrayList<Text>, and then iterate each element in ArrayList<Text>. But this > method is expensive because: > > 1) it calls VarCharVector.get(int index) which involves memory copy > 2) it calls Text.set(byte[]) which assemble the Text from byte array. > > My goal is just to retrieve each byte[] and do some filtering. Is there any > other less expensive method to achieve my goal? For example, > VarCharVector.get(int index, NullableVarCharHolder holder) seems to be a > less-expensive operation. But how to use this method in my case? > > Thanks again. > > Best regards, > Wenjian > > > > > On Wed, Aug 15, 2018 at 3:19 AM Wes McKinney <[email protected]> wrote: >> >> hi Wenjian, >> >> In C++ you can use ListBuilder together with UInt8Builder. There are >> examples of using ListBuilder you can look at in >> src/arrow/array-test.cc. >> >> For Java you might want to have a look at how Spark SQL converts its >> Array<T> types into Arrow (there should be other examples in the Java >> unit test suite, too): >> >> >> https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/arrow/ArrowWriter.scala >> >> - Wes >> >> On Mon, Aug 13, 2018 at 6:00 AM, Xu,Wenjian <[email protected]> wrote: >> > Hi, >> > >> > If I want to create list<list<byte>> structure (as shown in >> > https://arrow.apache.org/docs/memory_layout.html), what class(es) do I >> > need >> > to use in Java API and C++ API? >> > >> > Any suggestion would be appreciated. Thanks. >> > >> > Best regards, >> > Wenjian
