title: how to get value between points from a plot?
body: <p>Consider that I have the following sets of values,</p>
  
  <pre><code>Y = [1  23  4  67  89  23  5   12 ]
  X = [0  2   4  6   10  14  18  22 ]
  </code></pre>
  
  <p>I can draw a plot with the basic plot function. Now, from this plot, I want to know what the Y value for X=5. How can I get this data?</p>
  
  <p>You can see, it's not part of my plot points, but something I was to extract from the graph.</p>
  
  <p>Any ideas folks? I'm a bit surprised that there isn't a built in function for this.</p>