Implement mode function

[dmitrybugakov]

Which issue does this PR close?

Closes #12248

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[alamb]

RElated comment: #12254 (comment)

[dmitrybugakov]

Hi @alamb,

Could you help me choose the right approach?

I’ve started working on this issue. We chose "mode" as the first function for datafusion-functions-extra, but I’ve run into a challenge. My implementation involves patching ArrowBytesMap with new methods.

Should I first patch ArrowBytesMap and then wait for the new release of the DataFusion core, or is there a more efficient way to proceed?

[alamb]

Should I first patch ArrowBytesMap and then wait for the new release of the DataFusion core, or is there a more efficient way to proceed?

I would recommend:

1. Make a PR to update the new method
2. In the code of datafusion-functions-extra make a copy of ArrowBytesMap with the new methods you need with a link back to the PR that adds the APIs

That way you'll be unblocked but still have a path to avoid a second copy of the bytes map

[dmitrybugakov]

@alamb thank you!

[dmitrybugakov]

Implemented: mode.rs