Using Vega

Basic support for Vega graphics is supported as part of VegaLite.jl. Vega specifications are more verbose than VegaLite specifications, but with that verbosity comes more control/options - see the Vega documentation for details on creating Vega plots.

VegaLite.jl supports rendering Vega JSON specification graphics with interactivity via the REPL (launching a browser if available) or JupyterLab. There are two methods to do this: the vg_str macro or directly creating a VGSpec with parsed JSON.

The vg string macro

Similar to the vl string macro, the vg string macro takes the Vega spec as a JSON string and returns and renders a VGSpec.

using VegaLite

spec = vg"""
  {
  "$schema": "https://vega.github.io/schema/vega/v4.4.json",
  "width": 400,
  "height": 200,
  "padding": 5,

  "data": [
    {
      "name": "table",
      "values": [
        {"category": "A", "amount": 28},
        {"category": "B", "amount": 55},
        {"category": "C", "amount": 43},
        {"category": "D", "amount": 91},
        {"category": "E", "amount": 81},
        {"category": "F", "amount": 53},
        {"category": "G", "amount": 19},
        {"category": "H", "amount": 87}
      ]
    }
  ],

  "signals": [
    {
      "name": "tooltip",
      "value": {},
      "on": [
        {"events": "rect:mouseover", "update": "datum"},
        {"events": "rect:mouseout",  "update": "{}"}
      ]
    }
  ],

  "scales": [
    {
      "name": "xscale",
      "type": "band",
      "domain": {"data": "table", "field": "category"},
      "range": "width",
      "padding": 0.05,
      "round": true
    },
    {
      "name": "yscale",
      "domain": {"data": "table", "field": "amount"},
      "nice": true,
      "range": "height"
    }
  ],

  "axes": [
    { "orient": "bottom", "scale": "xscale" },
    { "orient": "left", "scale": "yscale" }
  ],

  "marks": [
    {
      "type": "rect",
      "from": {"data":"table"},
      "encode": {
        "enter": {
          "x": {"scale": "xscale", "field": "category"},
          "width": {"scale": "xscale", "band": 1},
          "y": {"scale": "yscale", "field": "amount"},
          "y2": {"scale": "yscale", "value": 0}
        },
        "update": {
          "fill": {"value": "steelblue"}
        },
        "hover": {
          "fill": {"value": "red"}
        }
      }
    },
    {
      "type": "text",
      "encode": {
        "enter": {
          "align": {"value": "center"},
          "baseline": {"value": "bottom"},
          "fill": {"value": "#333"}
        },
        "update": {
          "x": {"scale": "xscale", "signal": "tooltip.category", "band": 0.5},
          "y": {"scale": "yscale", "signal": "tooltip.amount", "offset": -2},
          "text": {"signal": "tooltip.amount"},
          "fillOpacity": [
            {"test": "datum === tooltip", "value": 0},
            {"value": 1}
          ]
        }
      }
    }
  ]
  }
  """

VGSpec

When parameterizing a Vega spec's data, the name of the data object must be specified, but the data can be passed to the object as below. URLs and file paths can also be specified using the (VGSpec)(data, name) syntax.

using VegaLite

data = [(category="A", amount=28),
    category="B", amount=55),
    category="C", amount=43),
    category="D", amount=91),
    category="E", amount=81),
    category="F", amount=53),
    category="G", amount=19),
    category="H", amount=87)]

vg"""
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"width": 400,
"height": 200,
"padding": 5,

"data": [
  {
    "name": "table"
  }
],

"signals": [
  {
    "name": "tooltip",
    "value": {},
    "on": [
      {"events": "rect:mouseover", "update": "datum"},
      {"events": "rect:mouseout",  "update": "{}"}
    ]
  }
],

"scales": [
  {
    "name": "xscale",
    "type": "band",
    "domain": {"data": "table", "field": "category"},
    "range": "width",
    "padding": 0.05,
    "round": true
  },
  {
    "name": "yscale",
    "domain": {"data": "table", "field": "amount"},
    "nice": true,
    "range": "height"
  }
],

"axes": [
  { "orient": "bottom", "scale": "xscale" },
  { "orient": "left", "scale": "yscale" }
],

"marks": [
  {
    "type": "rect",
    "from": {"data":"table"},
    "encode": {
      "enter": {
        "x": {"scale": "xscale", "field": "category"},
        "width": {"scale": "xscale", "band": 1},
        "y": {"scale": "yscale", "field": "amount"},
        "y2": {"scale": "yscale", "value": 0}
      },
      "update": {
        "fill": {"value": "steelblue"}
      },
      "hover": {
        "fill": {"value": "red"}
      }
    }
  },
  {
    "type": "text",
    "encode": {
      "enter": {
        "align": {"value": "center"},
        "baseline": {"value": "bottom"},
        "fill": {"value": "#333"}
      },
      "update": {
        "x": {"scale": "xscale", "signal": "tooltip.category", "band": 0.5},
        "y": {"scale": "yscale", "signal": "tooltip.amount", "offset": -2},
        "text": {"signal": "tooltip.amount"},
        "fillOpacity": [
          {"test": "datum === tooltip", "value": 0},
          {"value": 1}
        ]
      }
    }
  }
]
}
"""(data, "table")

Loading and saving vega specifications

The load and save functions can be used to load and save vega specifications to and from disc. The following example loads a vega specification from a file named myfigure.vega:

using VegaLite

spec = loadvgspec("myfigure.vega")

To save a VGSpec to a file on disc, use the save function:

using VegaLite

spec = ... # Aquire a spec from somewhere

savespec("myfigure.vega", spec)