Does today() exist in vega-lite?

Question

I'd like to show the difference between a date (Date1) from my data and "today" in my chart. I could add a column in my table that contains today's date, but I was wondering if I can somehow solve this in the transform [] statement to keep my tables lean.

Does something like:

today()

exist in vega-lite?

Answer 1

You can use the now() function within the vega-expression; see https://vega.github.io/vega/docs/expressions/#now

Here's a simple example of adding a column with today's date (open in editor):

{
  "data": {
    "values": [
      {"date": "2020-01-01T00:00:00"},
      {"date": "2021-01-01T00:00:00"},
      {"date": "2021-02-01T00:00:00"}
    ]
  },
  "transform": [{"calculate": "now()", "as": "today"}],
  "mark": "point",
  "encoding": {
    "x": {"field": "today", "timeUnit": "yearmonthdate", "type": "ordinal"},
    "y": {"field": "date", "timeUnit": "yearmonthdate", "type": "ordinal"}
  }
}