[docs] expand documentation on 'group' for ranking task

[jameslamb]

Based on the discussion in #3708 (comment), this PR proposes adding more details to the explanation of group in the Python and R packages.

I think that the current description doesn't give enough details for someone unfamiliar with LightGBM to get started. I know that I personally really struggled to understand what "group" should look like the first time I did learning-to-rank with LightGBM.

[StrikerRUS]

Very nice addition!
Could you please add ... , see `Query Data <#query-data>`__ section below for more info (or something like that) here

LightGBM/include/LightGBM/config.h

Line 674 in 68a40c7

// desc = **Note**: data should be grouped by query\_id

https://lightgbm.readthedocs.io/en/latest/Parameters.html#query-data

and unify that description at the bottom of the file with the proposed new one?

[jameslamb]

Very nice addition!
Could you please add ... , see `Query Data <#query-data>`__ section below for more info (or something like that) here

LightGBM/include/LightGBM/config.h

Line 674 in 68a40c7

// desc = **Note**: data should be grouped by query\_id

https://lightgbm.readthedocs.io/en/latest/Parameters.html#query-data
and unify that description at the bottom of the file with the proposed new one?

thanks for pointing me to that! I tried an update in 6a42dff, let me know what you think.

I built the docs locally like this

python helpers/parameter_generator.py
cd docs
make clean html

And confirmed that the link to the "Query Data" section worked as expected.

[StrikerRUS]

@jameslamb Yeah, thanks for updating general params doc! Please check my comments.

[StrikerRUS]

@jameslamb Thanks! I believe it's nice addition for beginners.

Feel free to merge after fixing typos below and regenerating Rds.

Some R documentation files have changed. Please re-generate them and commit those changes.

[jameslamb]

Thanks for catching my typos, sorry 😬

I just regenerated the R docs (ec63db8). Will merge this if / when Ci passes.

[github-actions]

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