Can't set unknown domain in colour scale

[rossburton]

I'm using the color scale with explicit domain/range to associate status names with colours:

  color: {
    type: "categorical",
    domain: ["success", "failed"],
    range: ["green", "red"]
  },

But status names I forgot to list come out invisible. A way of setting the unknown() value would be useful, it looks like it is hardcoded to undefined at

plot/src/scales/ordinal.js

Line 206 in 068f8d8

return ScaleO(scaleOrdinal().unknown(undefined), channels, {range, ...options});

.

[mbostock]

Anything outside the domain will not be plotted; we need the “other” transform for this use case.

[zanarmstrong]

I ran into something that seems similar related to NAs when plotting height / weight the Olympics dataset. Example here.

[Fil]

Another use-case (very similar to Zan's) can be found in https://observablehq.com/@rcatlord/spine-charts; for some of the areas (try "Rother" in the select), the value comes in as "NA" instead of a number, and the x axis switches to a categorical scale.

[Fil]

With this feature:

• In Zan's example the N/A can be shown by applying

  x: { unknown: 45 },
  y: { unknown: 10 }

• In rcatlord's example, the fix is a bit more complicated, since we need to coerce the scale to be quantitative:

x: {
  axis: "top",
  label: null,
  type: "linear",
  unknown: 650
}