[GitHub] [arrow] trxcllnt commented on issue #31458: [JS] Documentation is quite obscure and not useful

["trxcllnt (via GitHub)" <gi...@apache.org>]

trxcllnt commented on issue #31458:
URL: https://github.com/apache/arrow/issues/31458#issuecomment-1494961959

   @feefladder we have a few rudimentary column-wise `select()` and `assign()` routines on Table (and RecordBatch and Schema). This is written by hand so apologies if it doesn't compile, but here's how I'd implement something like that:
   
   ```typescript
   import {DataType, Vector, makeTable} from "apache-arrow"
   
   function* filter<T extends DataType>(vec: Vector<T>, pred: (x: T['TValue']) => boolean) {
     for (const val of vec) { yield pred(val); }
   }
   
   const src = makeTable({ name: ["Alice", "Bob"], otherColumn: [1, 2] });
   const dst = src.assign(makeTable({
     name: filter(src.getChild("name"), (x) => x === "bob")
   }));
   ```
   
   We explicitly wanted to enable using iterators like this, as there's lots of existing JS Iterator/AsyncIterator algorithm libraries (and even a [language proposal](https://github.com/tc39/proposal-iterator-helpers)!). So if instead you can use an iterator library like [IxJS](https://github.com/reactiveX/ixjs):
   ```typescript
   import {makeTable} from "apache-arrow";
   import {filter} from "ix/iterable/operators/filter";
   
   const src = makeTable({ name: ["Alice", "Bob"], otherColumn: [1, 2] });
   const dst = src.assign(makeTable({
     name: filter((x) => x === "bob")(src.getChild("name"))
   }));
   
   ```


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