Jorge created ARROW-10030: ----------------------------- Summary: [Rust] Support fromIter and toIter Key: ARROW-10030 URL: https://issues.apache.org/jira/browse/ARROW-10030 Project: Apache Arrow Issue Type: Improvement Reporter: Jorge
Proposal for comments: https://docs.google.com/document/d/1d6rV1WmvIH6uW-bcHKrYBSyPddrpXH8Q4CtVfFHtI04/edit?usp=sharing (dump of the proposal:) Rust Arrow supports two main computational models: # Batch Operations, that leverage some form of vectorization # Element-by-element operations, that emerge in more complex operations This document concerns element-by-element operations, that are the most common operations outside of the library. h2. Element-by-element operations These operations are programmatically written as: # Downcast the array to its specific type # Initialize buffers # Iterate over indices and perform the operation, appending to the buffers accordingly # Create ArrayData with the required null bitmap, buffers, childs, etc. # return ArrayRef from ArrayData We can split this process in 3 parts: # Initialization (1 and 2) # Iteration (3) # Finalization (4 and 5) Currently, the API that we offer to our users is: # as_any() to downcast the array based on its DataType # Builders for all types, that users can initialize, matching the downcasted array # Iterate # Use for i in (0..array.len()) # Use Array::value(i) and Array::is_valid(i)/is_null(i)` # use builder.append_value(new_value) or builder.append_null() # Finish the builder and wrap the result in an Arc This API has some issues: # value(i) +is unsafe+, even though it is not marked as such # builders are usually slow due to the checks that they need to perform # The API is not intuitive h2. Proposal This proposal aims at improving this API in 2 specific ways: * Implement IntoIterator Iterator<Item=T> and Iterator<Item=Option<T>> * Implement FromIterator<Item=T> and Item=Option<T> so that users can write: {code:java} let array = Int32Array::from(vec![Some(0), None, Some(2), None, Some(4)]); // to and from iter, with a +1 let result: Int32Array = array .iter() .map(|e| if let Some(r) = e { Some(r + 1) } else { None }) .collect(); let expected = Int32Array::from(vec![Some(1), None, Some(3), None, Some(5)]); assert_eq!(result, expected); {code} This results in an API that is: # efficient, as it is our responsibility to create `FromIterator` that are efficient in populating the buffers/child etc from an iterator # Safe, as it does not allow segfaults # Simple, as users do not need to worry about Builders, buffers, etc, only native Rust. -- This message was sent by Atlassian Jira (v8.3.4#803005)