How to transform object in mapper function

[VincentdeWit94]

Would it be possible to create a mapper function that returns a new object with new values?
Like we would do in JS:

.map((d) => ({a: d.alpha, b: d.beta}));
Which would return:
{ a: 'alpha_val', b: 'beta_val' }

Thanks!

[silentmatt]

Duplicate of #254.