title: Pandas get average and remove duplicate
body: <p>I have the following dataframe:</p>
  <pre><code>import pandas as pd
  df = pd.read_csv(...)
  </code></pre>
  <hr />
  <pre><code>A  B  C
  x  3  .
  x  5  . 
  x  1  .
  y  6  .
  y  4  .
  z  1  .
  z  1  .
  z  2  .
  z  4  .
  </code></pre>
  <p>Can someone tell me how can I achieve this:</p>
  <pre><code>A  B
  x  3
  y  5
  z  2
  </code></pre>
  <p><strong>1.</strong> Drop column C<br />
  <strong>2.</strong> Calculate the average based on column A<br />
  <strong>3.</strong> Remove duplicate rows based on column A</p>
  <p>It's my first adventure with python, sorry for spam - I tried to use others answers but nothing is working for me.</p>