title: gnuplot conditional plotting with if
body: <p>I have a data file with two columns </p>
  
  <pre><code>10  0.5
  20  0.8
  25  0.3
  15  0.6
  </code></pre>
  
  <p>I want to plot the second column if the first column is less than or equal 20. Problem is, I want to skip the rows where the first column is greater than 20, however gnuplot forces me to do something in the conditional part.</p>
  
  <p>The command is</p>
  
  <pre><code>plot 'data.txt' u ($1&lt;=20?$2:0) with points
  </code></pre>
  
  <p>As you can see, I have to specify to put a point of ZERO. I don't want that! I want to skip....</p>