title: gnuplot: plot multiple lines from single file and make title at end from column and key title manually
body: <p>I'm quite new with gnuplot and so maybe my question has an obvious answer. Please excuse if this is too noobish.</p>
  
  <p>I have the following data</p>
  
  <pre><code>20 500 1.0
  30 500 0.95
  40 500 0.85
  50 500 0.7
  60 500 0.5
  
  20 1000 1.1
  30 1000 1.05
  40 1000 0.95
  50 1000 0.8
  60 1000 0.6
  
  20 1500 1.2
  30 1500 1.15
  40 1500 1.05
  50 1500 0.9
  60 1500 0.7
  
  20 2000 1.26
  30 2000 1.22
  40 2000 1.13
  50 2000 0.99
  60 2000 0.79
  
  20 2500 1.33
  30 2500 1.29
  40 2500 1.21
  50 2500 1.06
  60 2500 0.88
  </code></pre>
  
  <p>Plotting this as a surface worked fine. Now I would like to plot this as 5 separate lines (using 1:3) and have the 2nd column as 'title at end' for each of the lines.</p>
  
  <p>I tried </p>
  
  <pre><code>plot "demo.dat" using 1:3:2 with lines title columnhead(2) at end
  </code></pre>
  
  <p>but this will only label the last line (which is bogus) with 500 and ignore all the others. Also it sets 500 as title in the key box (which I would like to set to another string). Is that possible or do I have to split the blocks into several files as suggested in <a href="https://stackoverflow.com/questions/24325128/how-to-plot-single-multiple-lines-depending-on-values-in-a-column-with-gnuplot">How to plot single/multiple lines depending on values in a column with GNUPlot</a> ?</p>