Add shelf constants syntax

[chrisgemignani]

We had an issue that looks like this

Howdy! I have advanced ingredients where I want values associated with the max date in my dataset. Right now, I am hard coding the date, but each time I load updated data, I have to adjust all my ingredients. Here’s an example:

kind: Measure
field: 'sum(Covid_Cases) / sum(if(Date="2020-10-12", F2F_Students___Staff)) * 1000'

The user wanted to be able to define a shelf where "2020-10-12" is the maximum date value in her dataset. The intent looks like this:

field: 'sum(Covid_Cases) / sum(if(Date=max(Date), F2F_Students___Staff)) * 1000'
format: ',.1f'
singular: 'Covid-19 Cases per 1,000 F2F

max(Date) would typically require a subquery.

A solution: Create a syntax for defining shelf constants. These would be simple calculations that could be performed before the shelf is evaluated. It should probably NOT take into account automatic filters.

Uses

• Find the max date in a dataset.
• Find the "top N" values in a dimension. This would enable creating a bucket with an other category.