title: D3 line transition starting at incorrect point
body: <p>I am working on my first d3 project and running into a seemingly simply issue.  </p>
  
  <p>I have tried to transition a line from point x1, y1 to x2, y2.  I would like to animate it to start at the first point and draw itself out to the second point.  </p>
  
  <p>The issue is that when my transition starts, it creates a line connecting x1, y1 to the top left corner of the window and then swings the whole line to connect to x2, y2.  </p>
  
  <p>If anyone could assist me in correcting the transition, that would be greatly appreciated!! </p>
  
  <pre><code>// adding the line  
  var lines = svg.selectAll("line")
      .data(dataset)
      .enter()
      .append("svg:line")
  
  // line attributes
  lines.attr(
             "x1", start_x)
             .attr("y1", start_y)
             .attr("x2", end_x)
             .attr("y2", end_y)
             .transition()
             .duration(600)             
  </code></pre>