ak.zip does not accept record objects

[agoose77]

Version of Awkward Array

main

Description and code to reproduce

Introduced by #2757

[jpivarski]

Copied from scikit-hep/fastjet#268 (comment):

I just saw your note, @agoose77: you consider it a regression but I don't! I don't think zipping over a record makes sense, since zipping is something that applies to collections. The same applies to the numerical scalars (msoftdrop, etc.).

• If all fields of the ak.zip are collections (of equal length), then that's the normal case, we know what to do.
• If some fields of the ak.zip are scalars (either records or numbers) and some are collections, then ak.zip should broadcast the scalars to the collections in order to be consistent, but that's not likely the user's intention. In this case, I thought it was pretty clear that only one overall value of msoftdrop, etc. is desired, not one per constituent.
• If all fields are scalars, ak.zip doesn't have any clear meaning. If you want a single record to be built from those scalars, use the ak.Record constructor (as in the second example above).

So ak.zip should at least refuse the all-scalars case and should probably exclude the some-scalars case. (Although I suppose that it's not excluding all-numbers right now.)

[agoose77]

I like this rationale! Closing.