descending shorthand

[mbostock]

Fixes #1458. This adds -name shorthand to the mark sort option, applying to both imputed ordinal scale domains and the basic sort transform.

There are still two more places where we could support -name shorthand: the stack transform’s order option, and the bin and group transform’s sort option. I guess I would like to support these, too, but it felt a bit burdensome to make more changes, so I’m hoping this can stand on its own.

[Fil]

It's very nice to use. I hope we can make the extra mile that will make it work everywhere there is sorting/ordering (tentatively #1606).

[mbostock]

This should wait for #1607 (at the very least for better testing, but also because that PR clarifies the desired behavior).

[mbostock]

Okay, I have merged with #1607, and also made the behavior more conservative: now the -channel shorthand only changes the default order option; it doesn’t attempt to invert the meaning of the given order if one is specified explicitly. I think this is easier to understand and simplifies the implementation slightly since we don’t need the reverseOrder wrapper.

It should be possible to extend this to the stack, group, and bin transforms. For the group and bin transforms, we’ll need some plumbing to change the ascendingDefined here to a dynamic comparator (descendingDefined or something custom):

plot/src/transforms/group.js

Lines 296 to 305 in 5c5acb7

	export function maybeSort(facets, sort, reverse) {
	if (sort) {
	const S = sort.output.transform();
	const compare = (i, j) => ascendingDefined(S[i], S[j]);
	facets.forEach((f) => f.sort(compare));
	}
	if (reverse) {
	facets.forEach((f) => f.reverse());
	}
	}

Similarly for the stack transform we’ll need plumbing to override the ascendingDefined here:

plot/src/transforms/stack.js

Lines 334 to 338 in 5c5acb7

	function applyOrder(stacks, O) {
	for (const stack of stacks) {
	stack.sort((i, j) => ascendingDefined(O[i], O[j]));
	}
	}

I feel this work is distracting from the release of 0.6.7 and tooltips, so I would ask that we do not work on extending this PR to stack, group, and bin transform today. I would like to get back to writing the documentation for 0.6.7 and determining if there is any additional blocking functionality (such as custom formats for crosshairs #1597).

[Fil]

I like how small the code change is. It's mostly docs and examples!