title: SettingWithCopyWarning message when transforming Datetime Date into String Python Dataframe
body: <p>I am receiving the following warning message when performing the following transformation of a date into a string:</p>
  
  <blockquote>
    <p>SettingWithCopyWarning:  A value is trying to be set on a copy of a
    slice from a DataFrame. Try using .loc[row_indexer,col_indexer] =
    value instead</p>
  </blockquote>
  
  <p>I am doing the following:</p>
  
  <pre><code>Data['Date'] = Data['Date'].dt.strftime('%Y-%m-%d')
  </code></pre>