[Lens] Shortcut functions that can be "exploded" to customize more

[wylieconlon]

From a user perspective, Lens already offers more than one way to configure queries (drag and drop, forms, suggestions, etc). We can also provide shortcut functions:

Shortcut function: A function that is composed of 2 or more underlying functions

The main reason to offer shortcut functions is to provide speed and allow users to learn the more powerful features. For example, one of the building blocks that we have identified is the math function. We have also talked about building a ratio function using math, which would be implemented as a Math function with a numerator and denominator.

Potential shortcut functions:

Name	How it's implemented
Filter ratio	Math function built on top of two metrics. Both metrics share the same function like "Average", but use different filters. The formatter is % by default.
Simple ratio	Math function built on top of two metrics, but filters are not required. The formatter is % by default.
Month over month	This is a shortcut for changing the date histogram interval to Month and applying a 1 month time offset, displayed as a percent. These steps can all be done separately to create other metrics like "Today vs 1 month ago"

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[wylieconlon]

Here's a gif showing the process the way I'm imagining it for filter ratio. Users can use the simplified editor for filter ratio, and then to make more detailed edits you click a contextual menu:

The main limitation of filter ratio is that you are required to use the same field on both numerator and denominator. This is what the "Ratio" implementation would look like, which supports multiple metrics:

cc @flash1293 @cchaos @AlonaNadler

[wylieconlon]

This issue still seems relevant, but we've changed the expected UX a bit. When you switch from a shortcut function to a formula, the formula will contain all of the sub-functions needed.

[flash1293]

The general feature is provided by formula - additions for quick functions should be added individually (there is an issue for filter ratio already)