Excellent demonstration! A suggestion here, to simplify (avoid the second derive) and generalize keys spreading after a fold. What about something like: // ex: 'new_sp_m2534'.match(/new_([a-z]{2})_(m|f)(\d+)/) .spread({key: d => op.jsmatch(d.key, /new_([a-z]{2})_(m|f)(\d+)/) }, { as: ['new', 'type', 'sex', 'age'] }) i know there is an op.match in Arquero, but it does not look equivalent to the js match function

Thanks, I've added an additional example below to demonstrate this.

Great, thanks for the op.match adjustment!

It looks like there's a spelling mistake: correponds → corresponds.

Fixed, thanks!