Building columns and tables

Many JavaScript application may only need to be able to load and iterate of the data in existing Apache Arrow files creating outside of JavaScript.

However a JS application may also want to create its own Arrow tables from scratch.

For this situation, Apache Arrow JS provides the makeBuilder() function that returns Builder instances that can be used to build columns of specific data types.

However, creating arrow-compatible binary data columns for complex, potentially nullable data types can be quite tricky.

import {Builder, Utf8} from 'apache-arrow';

const utf8Builder = makeBuilder({
  type: new Utf8(),
  nullValues: [null, 'n/a']
});

utf8Builder.append('hello').append('n/a').append('world').append(null);

const utf8Vector = utf8Builder.finish().toVector();

console.log(utf8Vector.toJSON());
// > ["hello", null, "world", null]