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https://issues.apache.org/jira/browse/ARROW-6583?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16931941#comment-16931941
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Arthur Maciejewicz commented on ARROW-6583:
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[~andygrove] thanks for the response, it certainly helps. I'll take a look
inside the compute kernels, and if I come up with something reusable, I may
send over a PR following the contributor guidelines.
I have also looked over DataFusion. I don't have really complex queries, mostly
I just need to: traverse a column at a time from a RecordBatch, compute some
summary statistics, and return offsets that subdivide the Array to do some
further computation. The ability to represent missing values is one of the
reasons I chose to build on this library.
I believe the statement of goals is very helpful, and I suggest perhaps placing
it in the README or generated docs in case another user might benefit from it.
I'll return to the mailing list for further questions if need be. Also thanks
to Wes as well for earlier direction.
> [Rust] Question and Request for Examples of Array Operations
> ------------------------------------------------------------
>
> Key: ARROW-6583
> URL: https://issues.apache.org/jira/browse/ARROW-6583
> Project: Apache Arrow
> Issue Type: Improvement
> Components: Rust
> Reporter: Arthur Maciejewicz
> Priority: Minor
>
> Hi all, thank you for your excellent work on Arrow.
> As I was going through the example for the Rust Arrow implementation,
> specifically the read_csv example
> [https://github.com/apache/arrow/blob/master/rust/arrow/examples/read_csv.rs]
> , as well as the generated Rustdocs, and unit tests, it was not quite clear
> what the intended usage is for operations such as filtering and masking over
> Arrays.
> One particular use-case I'm interested in is finding all values in an Array
> such that x >= N for all x. I came across arrow::compute::array_ops::filter,
> which seems to be similar to what I want, although it's expecting a mask to
> already be constructed before performing the filter operation, and it was not
> obviously visible in the documentation, leading me to believe this might not
> be idiomatic usage.
> More generally, is the expectation for Arrays on the Rust side that they are
> just simple data abstractions, without exposing higher-order methods such as
> filtering/masking? Is the intent to leave that to users? If I missed some
> piece of documentation, please let me know. For my use-case I ended up trying
> something like:
> {code:java}
> let column = batch.column(0).as_any().downcast_ref::<Float64Array>().unwrap();
> let mut builder = BooleanBuilder::new(batch.num_rows());
> let N = 5.0;
> for i in 0..batch.num_rows() {
> if column.value(i).unwrap() > N {
> builder.append_value(true).unwrap();
> } else {
> builder.append_value(false).unwrap();
> }
> }
> let mask = builder.finish();
> let filtered_column = filter(column, mask);{code}
> If possible, could you provide examples of intended usage of Arrays? Thank
> you!
>
>
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