Interactive Scatterplot Matrix

{
  "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
  "repeat": {
    "row": ["Horsepower", "Acceleration", "Miles_per_Gallon"],
    "column": ["Miles_per_Gallon", "Acceleration", "Horsepower"]
  },
  "spec": {
    "data": {"url": "data/cars.json"},
    "mark": "point",
    "selection": {
      "brush": {
        "type": "interval",
        "resolve": "union",
        "on": "[mousedown[event.shiftKey], window:mouseup] > window:mousemove!",
        "translate": "[mousedown[event.shiftKey], window:mouseup] > window:mousemove!",
        "zoom": "wheel![event.shiftKey]"
      },
      "grid": {
        "type": "interval",
        "resolve": "global",
        "bind": "scales",
        "translate": "[mousedown[!event.shiftKey], window:mouseup] > window:mousemove!",
        "zoom": "wheel![!event.shiftKey]"
      }
    },
    "encoding": {
      "x": {"field": {"repeat": "column"},"type": "quantitative"},
      "y": {"field": {"repeat": "row"},"type": "quantitative"},
      "color": {
        "condition": {
          "selection": "brush",
          "field": "Origin",
          "type": "nominal"
        },
        "value": "grey"
      }
    }
  }
}