Add note to prev expression return type for locf()

[cracksalad]

Description

After using interpolate() for years now, I used locf() for the first time and came across a difference in their prev parameters, precisely in their return types: While interpolate() expects a tuple like (time, value), locf() expects just a value. I thought that should also be noted in the docs (as is for interpolate() but not for locf()).

Links

No issue link, but link to current locf() doc: https://docs.timescale.com/api/latest/hyperfunctions/gapfilling/time_bucket_gapfill/#locf

Review checklists

Reviewers: use this section to ensure you have checked everything before approving this PR:

Subject matter expert (SME) review checklist

• Is the content technically accurate?
• Is the content complete?
• Is the content presented in a logical order?
• Does the content use appropriate names for features and products?
• Does the content provide relevant links to further information?

Documentation team review checklist

• Is the content free from typos?
• Does the content use plain English?
• Does the content contain clear sections for concepts, tasks, and references?
• Have any images been uploaded to the correct location, and are resolvable?
• If the page index was updated, are redirects required
  and have they been implemented?
• Have you checked the built version of this content?

[mkindahl]

I noted that we lack examples for using the prev argument for both locf and interpolate so it might be a good idea to add such examples and avoid confusion.

[cracksalad]

I noted that we lack examples for using the prev argument for both locf and interpolate so it might be a good idea to add such examples and avoid confusion.

Sounds like a good idea! I am willing to do that. Should I add another PR since this one is already approved?

[cracksalad]

Just added the two examples here. Could still move that to another PR, if you prefer.

[mkindahl]

I noted that we lack examples for using the prev argument for both locf and interpolate so it might be a good idea to add such examples and avoid confusion.

Sounds like a good idea! I am willing to do that. Should I add another PR since this one is already approved?

I have approved the text that you submitted, so you might want to submit this as a separate PR.

[mkindahl]

Just added the two examples here. Could still move that to another PR, if you prefer.

Just noted. Will check them.

[mkindahl]

LGTM, but I suggest some minor rewrites:

• "that is" and "for example" give a better flow of the text than "i.e." and "e.g."
• Would be nice with an elaboration, even if informal, why time is needed in one place and not the other. I added a suggestion, but feel free to modify it.
• The queries are using an exclusive range condition, so just checking that this was intentional and not a mistake.