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2d Density Plots in JavaScript

How to make a D3.js-based 2d density plot in JavaScript. Examples of density plots with kernel density estimations, custom color-scales, and smoothing.


New to Plotly?

Plotly is a free and open-source graphing library for JavaScript. We recommend you read our Getting Started guide for the latest installation or upgrade instructions, then move on to our Plotly Fundamentals tutorials or dive straight in to some Basic Charts tutorials.

// from http://bl.ocks.org/mbostock/4349187
// Sample from a normal distribution with mean 0, stddev 1.

function normal() {
    var x = 0,
        y = 0,
        rds, c;
    do {
        x = Math.random() * 2 - 1;
        y = Math.random() * 2 - 1;
        rds = x * x + y * y;
    } while (rds == 0 || rds > 1);
    c = Math.sqrt(-2 * Math.log(rds) / rds); // Box-Muller transform
    return x * c; // throw away extra sample y * c
}

var N = 2000,
  a = -1,
  b = 1.2;

var step = (b - a) / (N - 1);
var t = new Array(N), x = new Array(N), y = new Array(N);

for(var i = 0; i < N; i++){
  t[i] = a + step * i;
  x[i] = (Math.pow(t[i], 3)) + (0.3 * normal() );
  y[i] = (Math.pow(t[i], 6)) + (0.3 * normal() );
}

var trace1 = {
  x: x,
  y: y,
  mode: 'markers',
  name: 'points',
  marker: {
    color: 'rgb(102,0,0)',
    size: 2,
    opacity: 0.4
  },
  type: 'scatter'
};
var trace2 = {
  x: x,
  y: y,
  name: 'density',
  ncontours: 20,
  colorscale: 'Hot',
  reversescale: true,
  showscale: false,
  type: 'histogram2dcontour'
};
var trace3 = {
  x: x,
  name: 'x density',
  marker: {color: 'rgb(102,0,0)'},
  yaxis: 'y2',
  type: 'histogram'
};
var trace4 = {
  y: y,
  name: 'y density',
  marker: {color: 'rgb(102,0,0)'},
  xaxis: 'x2',
  type: 'histogram'
};
var data = [trace1, trace2, trace3, trace4];
var layout = {
  showlegend: false,
  autosize: false,
  width: 600,
  height: 550,
  margin: {t: 50},
  hovermode: 'closest',
  bargap: 0,
  xaxis: {
    domain: [0, 0.85],
    showgrid: false,
    zeroline: false
  },
  yaxis: {
    domain: [0, 0.85],
    showgrid: false,
    zeroline: false
  },
  xaxis2: {
    domain: [0.85, 1],
    showgrid: false,
    zeroline: false
  },
  yaxis2: {
    domain: [0.85, 1],
    showgrid: false,
    zeroline: false
  }
};
Plotly.newPlot('myDiv', data, layout);
Add slider controls to 2d-density-plot plots with the <a href="https://github.com/plotly/postMessage-API" target="_blank">postMessage API</a>.

See the <a href="https://jsfiddle.net/plotlygraphs/y9sdy76h/4/" target="_blank">code on JSFiddle</a>.

Watch <a href="https://raw.githubusercontent.com/plotly/documentation/gh-pages/all_static/images/flight_conflicts.gif" target="_blank">the 5 second video</a> of how it works.