Histogram Example

A histogram subdivides a numerical range into bins, and counts the number of data points with each segment. The resulting bar chart provides a discrete estimate of the probability density function.

Vega JSON Specification <>

{
  "$schema": "https://vega.github.io/schema/vega/v3.0.json",
  "width": 500,
  "height": 100,
  "padding": 5,

  "signals": [
    { "name": "binOffset", "value": 0,
      "bind": {"input": "range", "min": -0.1, "max": 0.1} },
    { "name": "binStep", "value": 0.1,
      "bind": {"input": "range", "min": 0.001, "max": 0.4, "step": 0.001} }
  ],

  "data": [
    {
      "name": "points",
      "url": "data/normal-2d.json"
    },
    {
      "name": "binned",
      "source": "points",
      "transform": [
        {
          "type": "bin", "field": "u",
          "extent": [-1, 1],
          "anchor": {"signal": "binOffset"},
          "step": {"signal": "binStep"},
          "nice": false
        },
        {
          "type": "aggregate",
          "key": "bin0", "groupby": ["bin0", "bin1"],
          "fields": ["bin0"], "ops": ["count"], "as": ["count"]
        }
      ]
    }
  ],

  "scales": [
    {
      "name": "xscale",
      "type": "linear",
      "range": "width",
      "domain": [-1, 1]
    },
    {
      "name": "yscale",
      "type": "linear",
      "range": "height", "round": true,
      "domain": {"data": "binned", "field": "count"},
      "zero": true, "nice": true
    }
  ],

  "axes": [
    {"orient": "bottom", "scale": "xscale", "zindex": 1},
    {"orient": "left", "scale": "yscale", "tickCount": 5, "zindex": 1}
  ],

  "marks": [
    {
      "type": "rect",
      "from": {"data": "binned"},
      "encode": {
        "update": {
          "x": {"scale": "xscale", "field": "bin0"},
          "x2": {"scale": "xscale", "field": "bin1",
                 "offset": {"signal": "binStep > 0.02 ? -0.5 : 0"}},
          "y": {"scale": "yscale", "field": "count"},
          "y2": {"scale": "yscale", "value": 0},
          "fill": {"value": "steelblue"}
        },
        "hover": { "fill": {"value": "firebrick"} }
      }
    },
    {
      "type": "rect",
      "from": {"data": "points"},
      "encode": {
        "enter": {
          "x": {"scale": "xscale", "field": "u"},
          "width": {"value": 1},
          "y": {"value": 25, "offset": {"signal": "height"}},
          "height": {"value": 5},
          "fill": {"value": "steelblue"},
          "fillOpacity": {"value": 0.4}
        }
      }
    }
  ]
}