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https://issues.apache.org/jira/browse/ARROW-1652?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16235775#comment-16235775
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ASF GitHub Bot commented on ARROW-1652:
---------------------------------------
TheNeuralBit commented on a change in pull request #1273: ARROW-1652: [JS]
housekeeping, vector cleanup
URL: https://github.com/apache/arrow/pull/1273#discussion_r148540215
##########
File path: js/src/types/table/row.ts
##########
@@ -0,0 +1,56 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements. See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership. The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License. You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied. See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+import { Vector, Struct } from '../types';
+import { VirtualVector } from '../vector/virtual';
+
+export class Row<TKey extends string | number> extends Vector {
+ readonly row: number;
+ readonly table: Struct<TKey>;
+ [Symbol.toStringTag]() { return 'Row'; }
+ constructor(table: Struct<TKey>, row: number) {
+ super();
+ this.row = row;
+ this.table = table;
+ }
+ get length() { return this.table.length; }
+ get<T = any>(key: TKey) {
+ const col = this.table.col(key as TKey);
+ return col ? col.get(this.row) as T : null;
+ }
Review comment:
@trxcllnt actually what I'm getting at here is something like the following:
```
let row = table.get(row_index);
let a = row.get('column_a'), b = row.get('column_b');
```
Each `get` call would result in a batch lookup in both the `column_a` and
`column_b` VirtualVectors even if the batch structure for both vectors is the
same. I'm just suggesting there could be a sub-class of `Row` that handles that
case. It could do the batch lookup once for the first call to `get` and re-use
it as a batch hint on subsequent calls.
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> [JS] Separate Vector into BatchVector and CompositeVector
> ---------------------------------------------------------
>
> Key: ARROW-1652
> URL: https://issues.apache.org/jira/browse/ARROW-1652
> Project: Apache Arrow
> Issue Type: Improvement
> Components: JavaScript
> Reporter: Brian Hulette
> Assignee: Paul Taylor
> Priority: Major
> Labels: Performance, pull-request-available
>
> CompositeVector should have a {{batch(..)}} function that returns a
> BatchVector
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