[Lens] Fitting functions

[flash1293]

Fixes #68403

This PR exposes the elastic-charts fitting functions (except for "Explicit") as a chart-level setting of the xy-chart.

The popover for now only contains a select for the fitting function, other options like color palette will be part of the same popover in a later iteration

If there is no line or area series, the select will be disabled (state will still be carried along)

For Pie charts there is no popover menu in the toolbar (if it gets added later because of other features, it won't contain the select at all)

Architecture

On an expression level, there is a new optional string argument fittingFunction on the lens_xy_chart, taking all available options. If no value is provided, it defaults to None, maintaining the old behavior - this means no migration is necessary, saved Lens visualizations will simply run an expression without a fittingFunction argument.

[flash1293]

Jenkins, test this.

[flash1293]

@elasticmachine merge upstream

[flash1293]

@wylieconlon @mbondyra This PR depends on #69263 which isn't merged yet, but besides that it's ready to review.

[flash1293]

Thanks for the second review round.

• Lowercased i18n ids
• I went with "Missing values: hidden" because it's short and easy to understand IMHO
• Slightly changed descriptions

To me it seems like there is enough uncertainty about wording to kindly ask @gchaps to weigh in. This PR adds the ability to configure how missing values in the chart are treated.

Each option has a name and a description:

This is what the user sees on an unconfigured chart:

This is how it looks like when the user can't configure this at the moment:

Open questions:

• Capitalization of the names - is lowercase the right choice here?
• Is "Missing values" understandable?
• Are the descriptions understandable?
• Are the option names understandable?

[timroes]

Capitalization of the names - is lowercase the right choice here?

I think as Wylie stated above, the actual labels should be camelcased. We usually never lowercase values in a select like that.

Is "Missing values" understandable?

I would have a slight tendency to put a verb in front of it, as Wylie suggested, like "Fit missing values" (or potentially "fit" is maybe a bit too "technical"): "Fill missing values"

[gchaps]

I agree that the text needs a verb in front of it. @timroes' suggestion for "Fill missing values" is good.

My vote is for init caps. That would also be consistent with how it's done in other apps.

"Carry", "Look ahead" (should be two words if you use it), and "Interpolate linearly" don't feel obvious to me. For the last, I'm wondering if we can come up with an easier explanation--and also make it consistent with the other descriptions.

Here is my suggestion.

Fill missing values

Hide
Do not fill gaps

Zero
Fill gaps with zeros

Linear
Fill gaps between values with a line
Fill gaps with a line

Average
Fill gaps with the average of the nearest values

Nearest
Fill gaps with the nearest value

Last
Fill gaps with the last value

Next
Fill gaps with the next value

[wylieconlon]

I was a bit confused about the difference between "Average" and "Linear", so I looked at the storybook example for this. This is what the "Average" option looks like:

This behavior is actually somewhat similar to what "Nearest" does:

Given these examples, it's my preference to actually remove both of these options from the menu. I think most users will be better served by "Linear".

[flash1293]

Thanks for your input @gchaps ! I applied your suggestions, this is how it looks now (ignore the weird colors):

@wylieconlon I think it's a good idea to start with just linear - the difference is very subtle in most cases and we can easily add more options if this becomes a common ask.

[flash1293]

@cchaos I think this is close enough for you to jump in with button styling if you want to (we can also do it on a separate PR - in that case could you check again and approve?)

[cchaos]

I can do a follow-up PR, but had a couple quick suggestions to get it a bit better in this PR.

[cchaos]

Let's just be explicit here. Also can you make the button similar to how you did the chart select?

Suggested change

	<EuiIcon type="gear" />
	Settings

[flash1293]

I played around a little with the styling but couldn't get it to a state I'm happy with - let's revisit this. I like the explicit Settings:

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 68f961d

Build metrics

@kbn/optimizer bundle module count

id	value	diff	baseline
lens	124	+9	115

History

• 💚 Build #58635 succeeded 653ae04
• 💔 Build #58615 failed efd751e
• 💚 Build #58302 succeeded f016ece
• 💚 Build #58194 succeeded ba332b3
• 💚 Build #57781 succeeded b48b8d6

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[flash1293]

As other work depends on this, I'm going to merge the PR with the two existing approvals. If someone has concerns feel free to raise them here and I will set up a follow up PR.