Density with dynamic split rules

density_drag_split.vg.json

{
  "$schema": "https://vega.github.io/schema/vega/v5.json",
  "background": "white",
  "padding": 5,
  "width": 400,
  "height": 300,
  "style": "cell",
  "data": [
    {
      "name": "source_0",
      "url": "data/cars.json",
      "format": {"type": "json"},
      "transform": [
        {
          "type": "kde",
          "field": "Horsepower",
          "counts": true,
          "steps": 100,
          "as": ["value", "density"]
        }
      ]
    },
    {
      "name": "splitvalues",
      "values": [
        {"x": 80},
        {"x": 160}
      ],
      "on": [
        {
          "trigger": "draggedMark",
          "modify":  "draggedMark",
          "values":  "dragTo"
        },
        {
          "trigger": "addMark",
          "insert":  "addMark"
        },
        {
          "trigger": "remMark",
          "remove":  "remMark"
        }
      ]
    }
  ],
  "signals": [
    {
      "name": "dragTo",
      "on": [{
        "events": "[@right_grabber:mousedown, window:mouseup] > window:mousemove",
        "update": "{x: invert('x',x())}"
      }]
    },
    {
      "name": "draggedMark",
      "on": [{
        "events": "@right_grabber:mousedown",
        "update": "group().datum"
      }]
    },
    {
      "name": "addMark",
      "on": [
        {
          "events": [
            {
              "source": "view",
              "type": "mousedown",
              "filter": "item().mark.name === 'root'"
            }
          ],
          "update": "{x: invert('x',x())}"
        }
      ]
    },
    {
      "name": "remMark",
      "on": [{
        "events": "@right_grabber:dblclick",
        "update": "group().datum"
      }]
    }
  ],
  "marks": [
    {
      "name": "layer_0_marks",
      "type": "line",
      "style": ["line"],
      "sort": {"field": "datum[\"value\"]"},
      "from": {"data": "source_0"},
      "encode": {
        "update": {
          "stroke": {"value": "#4c78a8"},
          "description": {
            "signal": "\"density: \" + (format(datum[\"density\"], \"\")) + \"; Horsepower: \" + (format(datum[\"value\"], \"\"))"
          },
          "x": {"scale": "x", "field": "value"},
          "y": {"scale": "y", "field": "density"},
          "defined": {
            "signal": "isValid(datum[\"value\"]) && isFinite(+datum[\"value\"]) && isValid(datum[\"density\"]) && isFinite(+datum[\"density\"])"
          }
        }
      }
    },
    {
      "name": "splitmarks",
      "type": "group",
      "from": {"data": "splitvalues"},
      "encode": {
        "enter": {"height": {"field": {"group": "height"}}},
        "update": {
          "x": [
            {
              "test": "!isValid(datum[\"x\"]) || !isFinite(+datum[\"x\"])",
              "value": 0
            },
            {"scale": "x", "field": "x"}
          ]
        }
      },
      "marks": [
        {
          "name": "layer_1_marks",
          "type": "rule",
          "style": ["rule"],
          "encode": {
            "update": {
              "strokeDash": {"value": [4, 6]},
              "stroke": {"value": "black"},
              "y": {"value": 0},
              "y2": {"field": {"group": "height"}}
            }
          }
        },
        {
          "type": "path",
          "name": "right_grabber",
          "encode": {
            "enter": {
              "y": {"field": {"group": "height"}, "mult": 0.5, "offset": -50},
              "fill": {"value": "#fff"},
              "stroke": {"value": "#666"},
              "cursor": {"value": "ew-resize"}
            },
            "update": {
              "path": {
                "signal": "'M0.5,33.333333333333336A6,6 0 0 1 6.5,39.333333333333336V60.66666666666667A6,6 0 0 1 0.5,66.66666666666667ZM2.5,41.333333333333336V58.66666666666667M4.5,41.333333333333336V58.66666666666667'"
              }
            }
          }
        }
      ]
    }
  ],
  "scales": [
    {
      "name": "x",
      "type": "linear",
      "domain": {"data": "source_0", "field": "value"},
      "range": [0, {"signal": "width"}],
      "nice": true,
      "zero": false
    },
    {
      "name": "y",
      "type": "linear",
      "domain": {"data": "source_0", "field": "density"},
      "range": [{"signal": "height"}, 0],
      "nice": true,
      "zero": true
    }
  ],
  "axes": [
    {
      "scale": "x",
      "orient": "bottom",
      "grid": false,
      "title": "value, data",
      "labelFlush": true,
      "labelOverlap": true,
      "tickCount": {"signal": "ceil(width/40)"},
      "zindex": 0
    },
    {
      "scale": "y",
      "orient": "left",
      "grid": false,
      "title": "density",
      "labelOverlap": true,
      "tickCount": {"signal": "ceil(height/40)"},
      "zindex": 0
    }
  ]
}