Simple Box Plot w/ Point Hover

README.md

A simple boxplot implementation in d3.js. Also see Jason Davies' implementation.

boxplot.js

//initialize the dimensions
var margin = {top: 10, right: 10, bottom: 10, left: 10},
    width = 800 - margin.left - margin.right,
    height = 100 - margin.top - margin.bottom,
    padding = 20
    midline = (height - padding) / 2;

//initialize the x scale
var xScale = d3.scale.linear()
               .range([padding, width - padding]);  

//initialize the x axis
var xAxis = d3.svg.axis()
              .scale(xScale)
              .orient("bottom");

//initialize boxplot statistics
var data = [],
    outliers = [],
    minVal = Infinity,
    lowerWhisker = Infinity,
    q1Val = Infinity,
    medianVal = 0,
    q3Val = -Infinity,
    iqr = 0,
    upperWhisker = -Infinity,
    maxVal = -Infinity;

d3.csv("data.csv", type, function(error,csv) { // load the data
  
  data = csv.map(function(d) {
    return d.value;
  });

  data = data.sort(d3.ascending);

  //calculate the boxplot statistics
  minVal = data[0],
  q1Val = d3.quantile(data, .25),
  medianVal = d3.quantile(data, .5),
  q3Val = d3.quantile(data, .75),
  iqr = q3Val - q1Val,
  maxVal = data[data.length - 1];
  // lowerWhisker = d3.max([minVal, q1Val - iqr])
  // upperWhisker = d3.min([maxVal, q3Val + iqr]);

  var index = 0;

  //search for the lower whisker, the mininmum value within q1Val - 1.5*iqr
  while (index < data.length && lowerWhisker == Infinity) {

    if (data[index] >= (q1Val - 1.5*iqr))
      lowerWhisker = data[index];
    else
      outliers.push(data[index]);
    index++;
  }

  index = data.length-1; // reset index to end of array

  //search for the upper whisker, the maximum value within q1Val + 1.5*iqr
  while (index >= 0 && upperWhisker == -Infinity) {

    if (data[index] <= (q3Val + 1.5*iqr))
      upperWhisker = data[index];
    else
      outliers.push(data[index]);
    index--;
  }
 
  //map the domain to the x scale +10%
  xScale.domain([0,maxVal*1.10]);

  var svg = d3.select("body")
              .append("svg")
              .attr("width", width)
              .attr("height", height);

  //append the axis
  svg.append("g")
     .attr("class", "axis")
     .attr("transform", "translate(0, " + (height - padding) + ")")
     .call(xAxis);

  //draw verical line for lowerWhisker
  svg.append("line")
     .attr("class", "whisker")
     .attr("x1", xScale(lowerWhisker))
     .attr("x2", xScale(lowerWhisker))
     .attr("stroke", "black")
     .attr("y1", midline - 10)
     .attr("y2", midline + 10);

  //draw vertical line for upperWhisker
  svg.append("line")  
     .attr("class", "whisker")
     .attr("x1", xScale(upperWhisker))
     .attr("x2", xScale(upperWhisker))
     .attr("stroke", "black")
     .attr("y1", midline - 10)
     .attr("y2", midline + 10);

  //draw horizontal line from lowerWhisker to upperWhisker
  svg.append("line")
     .attr("class", "whisker")
     .attr("x1",  xScale(lowerWhisker))
     .attr("x2",  xScale(upperWhisker))
     .attr("stroke", "black")
     .attr("y1", midline)
     .attr("y2", midline);

  //draw rect for iqr
  svg.append("rect")    
     .attr("class", "box")
     .attr("stroke", "black")
     .attr("fill", "white")
     .attr("x", xScale(q1Val))
     .attr("y", padding)
     .attr("width", xScale(iqr) - padding)
     .attr("height", 20);

  //draw vertical line at median
  svg.append("line")
     .attr("class", "median")
     .attr("stroke", "black")
     .attr("x1", xScale(medianVal))
     .attr("x2", xScale(medianVal))
     .attr("y1", midline - 10)
     .attr("y2", midline + 10);

  //draw data as points
  svg.selectAll("circle")
     .data(csv)     
     .enter()
     .append("circle")
     .attr("r", 2.5)
     .attr("class", function(d) {
      if (d.value < lowerWhisker || d.value > upperWhisker)
        return "outlier";
      else 
        return "point";
     })     
     .attr("cy", function(d) {
      return random_jitter();
     }) 
     .attr("cx", function(d) {
      return xScale(d.value);   
     })
     .append("title")
     .text(function(d) {
      return "Date: " + d.date + "; value: " + d.value;
     }); 

});

function random_jitter() {
  if (Math.round(Math.random() * 1) == 0)
    var seed = -5;
  else
    var seed = 5; 
  return midline + Math.floor((Math.random() * seed) + 1);
}

function type(d) {
  d.value = +d.value; // coerce to number
  return d;
}

data.csv

index.html

<!DOCTYPE html>
<link rel = "stylesheet" type="text/css" href="style.css" />
<style type="text/css"></style>
<html>
  <body>
    <script type="text/javascript" src="http://d3js.org/d3.v3.min.js"></script>
    <script type="text/javascript" src="boxplot.js"></script>      
  </body>
</html>

License.txt

This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to <http://unlicense.org>

style.css

body {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
}

.whisker line,
.median line,
.box rect, {
  fill: #fff;
  stroke: #000;
  stroke-width: 1px;
  shape-rendering: crispEdges;
}

circle {
  fill: black;
  stroke: none;
  shape-rendering: crispEdges;
}

circle:hover {
  fill: orange;
  stroke: orange;
  opacity: 1;
}

.outlier {
  stroke: black;
  stroke-width: 2px;
}

.point {  
  opacity: 0.25; 
}

.axis path {
    fill: none;
    stroke: black;
    stroke-width: 1px;
    shape-rendering: crispEdges;
}

.axis line {
    fill: none;
    stroke: black;
    stroke-width: 1px;
    shape-rendering: crispEdges;
}

.axis text {    
    font-size: 10px;
}

thumbnail.png

you have written the example for single box, what should be the position of y1 and y2 if there are multiple boxes. I am facing this issue because I have implemented the same code for mutiple data. But i am not able to figure out how to set the position based on the tick marks and the scale is an ordinal scale.

Could you please help me in this?