{ "$schema": "https://vega.github.io/schema/vega-lite/v4.json", "data": {"url": "data/cars.json"}, "selection": { "pts": {"type": "single"} }, "mark": "rect", "encoding": { "y": {"field": "Origin"}, "x": {"field": "Cylinders"}, "color": { "condition": { "selection": "pts", "aggregate": "count" }, "value": "grey" } }}