Density visualizations with group by are not stacking correctly

[domoritz]

Open the Chart in the Vega Editor

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "width": 400,
  "height": 100,
  "data": {
    "url": "data/cars.json"
  },
  "mark": "area",
  "transform": [
    {
      "fold": ["Displacement", "Horsepower"],
      "as": ["measurement", "value"]
    },
    {
      "density": "value",
      "groupby": ["measurement"]
    }
  ],
  "encoding": {
    "x": {"field": "value", "type": "quantitative"},
    "y": {"field": "density", "type": "quantitative", "stack": "zero"},
    "color": {"field": "measurement", "type": "nominal"}
  }
}

[domoritz]

The issue is that we use impute to fill in missing densities as 0 but the densities are not aligned.

It works if we set the extent explicitly.

Open the Chart in the Vega Editor

[joelostblom]

This is currently working as intended, so I'm closing the issue. I believe it was solved in #9106