title: Gnuplot: How to load and display single numeric value from data file
body: <p>My data file has this content</p>
  
  <pre><code># data file for use with gnuplot
  # Report 001
  # Data as of Tuesday 03-Sep-2013 
  total   1976
  case1   522 278 146 65  26  7
  case2   120 105 15  0   0   0
  case3   660 288 202 106 63  1
  </code></pre>
  
  <p>I am making a histogram from the case... lines using the script below - and that works.  My question is: how can I load the grand total value 1976 (next to the word 'total') from the data file and either (a) store it into a variable or (b) use it directly in the title of the plot?</p>
  
  <p>This is my gnuplot script:</p>
  
  <pre><code>reset
  set term png truecolor
  set terminal pngcairo size 1024,768 enhanced font 'Segoe UI,10'
  set output "output.png"
  set style fill solid 1.00
  set style histogram rowstacked
  set style data histograms
  set xlabel "Case"
  set ylabel "Frequency"
  set boxwidth 0.8
  plot for [i=3:7] 'mydata.dat' every ::1 using i:xticlabels(1) with histogram \
  notitle, '' every ::1 using 0:2:2 \
  with labels \
  title "My Title"
  </code></pre>
  
  <p>For the benefit of others trying to label histograms, in my data file, the column after the case label represents the total of the rest of the values on that row.  Those total numbers are displayed at the top of each histogram bar.  For example for case1, 522 is the total of (278 + 146 + 65 + 26 + 7).</p>
  
  <p>I want to display the grand total somewhere on my chart, say as the second line of the title or in a label.  I can get a variable into sprintf into the title, but I have not figured out syntax to load a "cell" value ("cell" meaning row column intersection) into a variable. </p>
  
  <p>Alternatively, if someone can tell me how to use the sum function to total up 522+120+660 (read from the data file, not as constants!) and store that total in a variable, that would obviate the need to have the grand total in the data file, and that would also make me very happy.</p>
  
  <p>Many thanks.</p>