Is it possible to have columns of donut chart with gray arc indicating the missing part? - vega-lite

Question

Currently, the donut chart assumed that the max value is 100%. What I would like is for the category Chinese to have a percentage of 50% with gray arc indicating the missing 50%. The two other donut charts will behave similarly in their respective column.
{
"$schema": "https://vega.github.io/schema/vega-lite/v4.json",
"description": "A simple donut chart with embedded data.",
"data": {
"values": [
{"category": "English", "value": 4},
{"category": "Malay", "value": 6},
{"category": "Chinese", "value": 10}
]
},
"mark": {"type": "arc", "innerRadius": 80},
"encoding": {
"column": {"field": "category"},
"theta": {"field": "value", "type": "quantitative"},
"color": {"field": "category", "type": "nominal"}
},
"view": {"stroke": null}
}

Answer 1

It's a bit more complex, but one way to do this is to use a transform to calculate the total, and then a layer chart to plot that total in the background.
Here is an example (open in editor):
{
"data": {
"values": [
{"category": "English", "value": 4},
{"category": "Malay", "value": 6},
{"category": "Chinese", "value": 10}
]
},
"transform": [
{"joinaggregate": [{"op": "sum", "field": "value", "as": "total"}]}
],
"facet": {"column": {"field": "category"}},
"spec": {
"layer": [
{
"mark": {"type": "arc", "innerRadius": 80, "color": "lightgray"},
"encoding": {"theta": {"field": "total", "type": "quantitative"}}
},
{
"mark": {"type": "arc", "innerRadius": 80},
"encoding": {
"theta": {"field": "value", "type": "quantitative"},
"color": {"field": "category"}
}
}
],
"view": {"stroke": null}
}
}