title: Add values in column of Panda Dataframe
body: <p>I want to add up the values for a particular column. 
  I have a dataframe loaded from CSV that contains the following data: </p>
  
  <pre><code>  Date    Item  Count Price per Unit     Sales
  0  1/21/16  Unit A     40         $1.50    $60.00
  1  1/22/16  Unit A     20         $1.50    $30.00
  2  1/23/16  Unit A    100         $1.50   $150.00
  </code></pre>
  
  <p>I want to add up all the sales. I've tried:</p>
  
  <pre><code>print sales_df.groupby(["Sales"]).sum()
  </code></pre>
  
  <p>But it's not adding up the sales. What can I do to make this work? </p>