title: How to plot bar for 3 series with multiple samples
body: <p>My question is how to plot a bar graphic to compare 3 variables where I have a set of samples. Suppose the variables are temperatures and so, I can have the following data frame</p>
  
  <pre><code>    T1     T2     T3
      1.04   0.72   0.74
      0.23   0.32   0.55
      0.78   0.40   1.22
      220    210    213
      1.3    0.9    1.2
  </code></pre>
  
  <p>And I want to get something like this picture (I tried change a sample graphic to try explain what I need):</p>
  
  <p><img src="https://i.stack.imgur.com/JHzyz.jpg" alt="enter image description here"></p>
  
  <p>The idea is to have 3 bar plotted for each sample line.
  I tried to use <code>ggplot</code> but had no success trying to generate the graphic. Maybe I need to rearrange the samples in groups or something similar.
  Regards.</p>