title: Plot from csv with panda grouping
body: <p>If I have a csv with 4 columns:
  how can I average the values of one column (x) over the average of another column (y) by grouping through the first one with panda? I have to do a loop for every value of the first column? I am not sure about the implementation.</p>
  <p>For example, if I have a csv file:</p>
  <p>a,1,2,4<br />
  a,2,2,5<br />
  a,3,2,6<br />
  a,4,2,5<br />
  b,1,3,2<br />
  b,2,3,3<br />
  b,3,3,4</p>
  <p>and I want a plot with a,average(3rd column) and b,average(3rd column)</p>
  <p>I have to do something like:</p>
  <pre><code>df=pd.reas_csv
  x=group_by(&quot;values of the 1st column&quot;).average()
  </code></pre>
  <p>I would also try to plot kde over the 2nd column, which has ten rows for every group of the first column.
  I don't understand how to group data from *csv file without a header in particular.</p>
  <p>Thank you for the help.</p>