title: Create duplicate column in pandas dataframe
body: <p>I want to duplicate a column which has numerical character in the start position. ie(<strong>1</strong>stfloor)</p>
  <p>In simple term, I want to convert column 1stfloor to FirstFloor</p>
  <pre><code>df
      1stfloor
      456 
      784
      746
      44 
      9984
  </code></pre>
  <p>Tried using the below code,</p>
  <pre><code>df['FirstFloor'] = df['1stfloor']
  </code></pre>
  <p>encountered with below error message:</p>
  <p>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>
  <p><strong>Expected output:</strong></p>
  <p>df</p>
  <pre><code>FirstFloor 
  456 
  784
  746
  44 
  9984
  </code></pre>