multiple inside guide box with different position

[Yunuuuu]

Try to fix #5712.

This enables users to set legend.position.inside and legend.justification.inside in theme of guide_legend and guide_colourbar.

Here is an example:

ggplot(mpg, aes(displ, hwy, shape = drv, colour = cty, size = year)) +
    geom_point(aes(alpha = cyl)) +
    guides(
        colour = guide_colourbar(
            position = "inside",
            theme = theme(legend.position.inside = c(1, 0))
        ),
        size = guide_legend(position = "top"),
        alpha = guide_legend(
            position = "inside",
            theme = theme(legend.position.inside = c(0, 1))
        ),
        shape = guide_legend(position = "left")
    )

[teunbrand]

Hi Yunuuuu, thanks for preparing a PR for this issue!

The PR appears to break a visual test for the alignment of legends with the inside position. It is important to us to preserve current behaviour without regressions.

Next, it is hard to tell from the PR what the assembly rules for inside legends are. When legends share legend.position.inside values, they merge (are placed in the same guide-box). It seems that justification also factors into this and I'm not convinced that it should. It'd be great if the logic for this is expressed more clearly, perhaps through code comments.

Lastly, there are a few fussy changes to the code I'd like to propose, but it'd make more sense to go over this after the PR adresses the previous points.

[Yunuuuu]

@teunbrand Thank you for the reviewing. I have made the following changes based on your feedback:

1. Added more comments and explanations throughout the code to improve clarity.
2. Fixed the test error that was identified.
3. Merged the guide legends based solely on legend.position.inside, as it seems sufficient to identify the legend groups.

[Yunuuuu]

I'll check it

[Yunuuuu]

Should we always keep the inside guide box, even if there are no inside guide legends?

[teunbrand]

Should we always keep the inside guide box, even if there are no inside guide legends?

An empty inside guide box should give a zeroGrob() for consistency in gtable layout

[Yunuuuu]

should fixed

[teunbrand]

Thanks for getting the PR to work!
My overall feeling about this PR is that it is a little bit on the more invasive side, whereas I think it could be more surgical than it currently is.
If we lift the responsibility of managing the positions into Guides$assemble(), we should have to change less code elsewhere.

[Yunuuuu]

I'll try to make some new changes

[Yunuuuu]

Thank you for your thorough review and all the valuable advice.

[Yunuuuu]

After writing some examples, I’ve realized that it’s necessary to allow users to set the inside justification for each inside legend. In this way, it would be beneficial for splitting legends based on their justifications, as users may be confused about which justification will be applied if we only split legends with the same inside position into groups.

[Yunuuuu]

I’m unable to run the tests on my local machine, as there are always some errors. I’m unable to update the test snapshots.

[teunbrand]

Thanks for all the changes, Yunuuuu!
I apologise but I still have a few more to suggest. I'd be happy to help out trying to find a solution for not editing Guides$package_box() as much as is reasonable.

I’m unable to update the test snapshots.

I'm happy to do this for you if you like.

[Yunuuuu]

Thanks for the reviewing, I'll take a look tonight.

[Yunuuuu]

Thanks for your suggestions! the code looks much cleaner.

I'm happy to do this for you if you like.

Thank you! I need your help to update the test snapshots

[teunbrand]

This looks a lot more self-contained than before so thank you for putting up with all the comments I had and putting all the work into this PR. In principle I think this PR is in the right shape but I have two brief points:

• If you like, you can add a news bullet to the NEWS.md file with a short description of what is new, what issue it solved and your github handle.
• Would you mind if I make a few small tweaks here and there, mostly for readability purposes?

[Yunuuuu]

Would you mind if I make a few small tweaks here and there, mostly for readability purposes?

Feel free to make any tweaks you think would improve readability. I appreciate your help!

[Yunuuuu]

If you like, you can add a news bullet to the NEWS.md file with a short description of what is new, what issue it solved and your github handle.

I'll add this

[teunbrand]

Thanks for adding the bullet! Are the tweaks I made OK to you or should I roll back some changes?

[Yunuuuu]

Thanks for the thoughtful guidance and review process. Everything works perfectly on my end!

[teunbrand]

Great, thank you for the contribution!

[neellab-umd]

This is ability to place legends separately inside a plot is an excellent improvement! Thank you both so much for making it happen! Do you know when it will go live?

[teunbrand]

Well you can download the development version now to try it out, instructions are in the readme. It will probably be sent to CRAN a few months into 2025.

[neellab-umd]

Thank you! That is great. This really helps for placing legends around data in graphs and especially placing them around geographic features on maps.