Fetch values for components

[vhf]

Fixes #20

TODO:

• [x] fetch distinct values
• [x] fetch min/max values
• [x] try to be smart about it
• [x] tests
• [ ] jsdoc/typedoc
• [ ] doc

[vhf]

Sure, I could implement it on Dimension/Attribute/Measure and we'd use it like this:

myDimension.values()

source

Turns out values depend on the data cube so I came up with a different API:

https://github.com/zazuko/query-rdf-data-cube/blob/cefd4e576f7030abdc07c16687f82fbf7d7519d3/examples/component-values.ts#L14-L45

https://github.com/zazuko/query-rdf-data-cube/blob/cefd4e576f7030abdc07c16687f82fbf7d7519d3/examples/component-values-min-max.ts#L10-L29

Could you please comment on that @ktk @herrstucki @lucguillemot?

[jstcki]

Awesome, looks good to me!

I wonder if additionally adding the possibility to add this to queries as well would be possible (like i described in https://github.com/zazuko/query-rdf-data-cube/issues/20#issuecomment-530817209):

// All dimension values of a cube
await cube.componentValues(myDimension) // => [1,2,3,4,5]

// Construct query without executing
const query = cube.query().filter(something)

// All dimension values of this query
await query.componentValues(myDimension) // => [3,5]

[vhf]

Sounds like something useful, I'll try to implement it and come back to you for feedback on the API, it might diverge a bit from your example.

[ktk]

@vhf lgtm, if it's useful for IXT I'm good :)