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2d Density Plots in plotly.js

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.

// 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.