title: Histogram (plotting count data)
body: <p>I want to plot histogram with 6 classes. I tried without success.</p>
  
  <p>my data :</p>
  
  <pre><code>      1  2  4  6  7  8  9 10 11 12 13 14 15 16 #1st row score
        1  1  2  2  1  4  2  3  3  2  1  3  3  2 #2d frequency (number of persons how obtained this score )
  </code></pre>