Do you need a dynamic bar chart like this in your web page, with positive and negative values, and categories along the x-axis?

Dog breeds are on my mind at the moment as we just bought a new Sheltie puppy – this chart might show a person’s scores for each breed. Click the button above to see the next person’s (random) set of scores.

This is an example of a reusable chart built using d3. Using it is fairly simple, eg.:

<script src="http://d3js.org/d3.v3.min.js"></script>
<script src="barChart.js"></script>
<script>
    var points = [['Beagle',-10],
                  ['Terrier',30],
                  ['Sheltie',55],
                  ['Greyhound',-24]];
    var myChart = d3.elts.barChart().width(300);
    d3.select("body").datum(points).call(myChart);
</script>

Please check out the source code for barChart.js on bitbucket.

You may also find this helpful even if you don’t need a barchart, but want to understand how to build a reusable chart. I was inspired when I read Mike Bostock’s exposition, Towards reusable charts, but I found it took some work to get my head around how to do it for real – so I hope this example may help others too.

The key tricks were:

• How to adjust Mike Bostock’s sample code to produce bars instead of a line and area
• Where the enter(), update and exit() fit in (answer: they are internal to the reusable function)
• How to call it, including whether to use data vs datum (answer: see code snippet above)
• How to refer to the x and y coordinates inside the function (answer: the function maps them to d[0] and d[1] regardless of how they started out)

You can find a much fancier version of this chart, with a range slider and hover text, in this post.

Good luck!