D3 Examples - D3 Barchart, multiple datasets, updating on select (Data: breathalyser test counts per month)

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Data &amp; Colour Example</title>
    <script src="//d3js.org/d3.v4.min.js"></script>
    <style>
        html, body, #vis {
            height: 100%;
            margin: 0;
        }
    </style>
</head>
<body>
    <form>
        <select name="year" id="year">
            <option value="2009">2009</option>
            <option value="2010">2010</option>
            <option value="2011">2011</option>
            <option value="2012">2012</option>
            <option value="2013">2013</option>
            <option value="2014" selected>2014</option>
        </select>
    </form>
    <div id="vis"></div>
    <script src="script.js">
    </script>
</body>
</html>
    