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vega-lite

Dynamic scale domain in vega-lite

I would like to define my x-axis:

  • minimum value should be now()

  • maximum value should be automatically determined (just as if the domain of the scale would have not been defined)

       "encoding": {
 "y": {
   "field": "Reference",
   "type": "nominal",
   },
 "x":{
   "field": "Date",
   "type": "temporal",
   "scale": {"domain": [now(), 1618000000000]}}

I also tried to use an expression to set-up now(), to no success:

"scale": {"domain": ["expr":"now()", 1618000000000]
Solution

  • You were quite close with the second attempt; you just need to put braces around the expression statement:

    "scale": {"domain": [{"expr": "now()"}, "2021-05-01T00:00:00"]}

    Here's a full example (open in editor):

    {
  "data": {
    "values": [
      {"date": "2021-03-01T00:00:00", "value": 1},
      {"date": "2021-04-01T00:00:00", "value": 3},
      {"date": "2021-05-01T00:00:00", "value": 2}
    ]
  },
  "mark": "line",
  "encoding": {
    "x": {
      "field": "date",
      "type": "temporal",
      "scale": {"domain": [{"expr": "now()"}, "2021-05-01T00:00:00"]}
    },
    "y": {"field": "value", "type": "quantitative"}
  }
}

    enter image description here

    If instead of setting the domain limits, you just want to ensure that now() appears as part of the domain, you can use a domain unionWith statement:

    "scale": {"domain": {"unionWith": [{"expr": "now()"}]}}

    This will create an automatically calculated domain that contains the current date.