title: How to label (x,y) data points in Gnuplot 4.2 with integer numbers
body: <p>I have a text file with 2 columns of numbers corresponding to (x,y) coords.</p>
  
  <pre><code>4 1
  4 5
  1 1
  1 5
  2.5 3
  </code></pre>
  
  <p>How do I tell gnuplot to plot these points and label each point with its corresponding row #?  (Please keep in mind I'm going to apply this to a much larger file with 100 points, so I'm looking for a way to do it automagically, rather than have to create a 3rd column of data corresponding to row numbers).</p>