title: Pandas: plot the graph of unique values
body: <p>I have a column in pandas dataframe: </p>
  
  <pre><code>df.['A']:
  1
  1
  1
  2
  2
  3
  1
  2
  3
  1
  2
  3
  </code></pre>
  
  <p>I need to plot a histogram which will show how much if 1, of 2 and of 3 i have.
  For that i firstly count the amount of all 1, 2, and 3:</p>
  
  <pre><code>print df.groupby(df.index)['A'].nunique()
  </code></pre>
  
  <p>but instead of getting</p>
  
  <pre><code>1   5
  2   4
  3   3
  </code></pre>
  
  <p>i get</p>
  
  <pre><code>1
  1
  1
  </code></pre>
  
  <p>what is my mistake? and may be there is a better way of plotting it withpout previous extraction of counted data?</p>