title: D3 linechart string domain x-axis
body: <p>I'm relatively new to D3, and I can't figure out why something isn't working.
  I want to draw a line-chart with d3, and this works fine, but I have problems with the axes.</p>
  
  <p>With the following code it goes wrong somewhere and I don't see how to solve...</p>
  
  <pre><code>var x = d3.scale.linear()
  .range([0, width]);
  
  var xAxis = d3.svg.axis()
  .scale(x)
  .orient("bottom");
  
  x.domain(d3.extent(data, function(d) { return d.age; }));
  </code></pre>
  
  <p>If <code>d.age</code> is an integer (like <code>1;2;3</code> etc.), it works well. But I want strings on the x-axis. Like <code>("netherlands", "England", "Belgium")</code>.</p>
  
  <p>So if <code>d.age</code> is an integer it draws the graph OK, if d.age is a string it doesn't draw anything.</p>
  
  <p>I have also tried instead of linear to use ordinal, but this gave an incorrect chart. (Weird looking lines...).</p>