[Docs] Dynamic filters

[antonymilne]

Description

Docs for #879.

As discussed in #461, our current load_iris_data example is not very inspiring and we should change it or come up with a second more advanced example. For now I've kept it the same though. Let's update once we've got parametrised data filters fully working.

Please review:
@petar-qb - have I missed anything?
@maxschulz-COL @huong-li-nguyen does it make sense? Some of it was hard to explain so would be great if someone who has not been so deep in the weeds on this could read through it.
@stichbury the usual 🙂

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[huong-li-nguyen]

Really exciting! 💯 🚀 Amazing job you two @petar-qb @antonymilne!

Overall well written and clear, but one thing where I still have an open question is what happens with a page with two charts, drawn from different data sources, one dynamic and one static.

In general, do we have anywhere in the docs that the Filter takes the union of values, if the selected column is present in two data sources?

[antonymilne]

Thanks for the review @huong-li-nguyen, it's super helpful to get a fresh pair of eyes on this!

Overall well written and clear, but one thing where I still have an open question is what happens with a page with two charts, drawn from different data sources, one dynamic and one static.

In general, do we have anywhere in the docs that the Filter takes the union of values, if the selected column is present in two data sources?

Hmm, good point - not really as far as I can see. On the filters docs page we say "By default, all components on a page with such a column present will be filtered. The selector type will be chosen automatically based on the target column, for example, a dropdown for categorical data, a range slider for numerical data, or a date picker for temporal data." But there's nothing explaining how the range/options itself are found from the union of values. Let me add this!

[stichbury]

LGTM from a docs perspective 🌟 🌟 🌟 🌟 🌟

I left a few comments and suggestions for tweaks but I'm super happy with this and don't need to see them again. Approving 🙏

[maxschulz-COL]

LGTM! Pretty cool functionality 🚀

[petar-qb]

Great work! 🥇

[petar-qb]

Thanks for addressing the comments. I reviewed it again and I think this PR is ready for merging.

The only remaining minor thing that maybe could be improved is swapping the following two sections:
"Override selector options to make a dynamic filter static" and "Dynamic filter with specific selector is still dynamic". Just consider this and ignore if irrelevant 😃

[antonymilne]

@petar-qb I tried swapping those round and found it made things worse overall because the last section on "filters that depend on parametrized dynamic data loading" became less clear as it sounded like it worked with static data, which didn't make sense. And it also didn't make sense to move that section further up the page.

@huong-li-nguyen added explanation of how filters choose options and min/max in 2c307d7. In fact the whole bit on filter default selectors was on the wrong page (since it only applies to filters, not selectors in general), so I moved it.