Feature request: "day of year" timeUnit

It would be nice if it were possible to compute the day of year as a timeUnit. Here is how it can be calculated using a series of transforms:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "data": {"url": "data/seattle-weather.csv"},
  "transform": [
    {"timeUnit": "yearmonthdate", "field": "date", "as": "date"},
    {"timeUnit": "year", "field": "date", "as": "start"},
    {"calculate": "round((datum.date - datum.start) / (24 * 60 * 60 * 1000), 1)", "as": "dayOfYear"}
  ],
  "mark": "rect",
  "encoding": {
    "x": {"field": "dayOfYear", "type": "ordinal", "title": "day of year"},
    "y": {"field": "date", "timeUnit": "year", "type": "ordinal", "title": "year"},
    "color": {"field": "temp_max", "type": "quantitative"}
  },
  "width": 800
}

It would be nicer if the above chart could be expressed as something like this:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "data": {"url": "data/seattle-weather.csv"},
  "mark": "rect",
  "encoding": {
    "x": {"field": "date", "timeUnit": "dayofyear", "type": "ordinal", "title": "day of year"},
    "y": {"field": "date", "timeUnit": "year", "type": "ordinal", "title": "year"},
    "color": {"field": "temp_max", "type": "quantitative"}
  },
  "width": 800
}

[domoritz]

@jakevdp https://github.com/vega/vega-lite/issues/6349

[jheer]

I just added a dayofyear unit in this Vega PR: https://github.com/vega/vega/pull/2530

Also, Vega supports both week (week) and day of week (day) units that I think you should be able to use for a nice cross-tab, assuming Vega-Lite exposes those.

I don’t think we’d support a complement, in part because as I don’t know how that should handle all the fields of full date-times (with hours, milliseconds, etc).