title: Using math package (e.g. math.radians, math.tan) on pandas dataframe column
body: <p>Example df:</p>
  
  <pre><code>data = pd.DataFrame({'col1': ['1.55', '2.22', '2.22', '3.33'],
                    'col2': ['10', '15', '20', '30']})
  </code></pre>
  
  <p>I want to add a new column using some math functions on <code>col1</code>, e.g.</p>
  
  <pre><code>data['new'] = math.radians(data['col1'])
  </code></pre>
  
  <p>or</p>
  
  <pre><code>data['new'] = math.tan(data['col1'])
  </code></pre>
  
  <p>This gives me the error <code>TypeError: cannot convert the series to &lt;class 'float'&gt;</code>. I have converted <code>col1</code> to float using <code>data['col1'] = data['col1'].astype(float64)</code>, so I think the error must be because <code>data['new']</code> cannot be converted to float. </p>
  
  <p>How can I fix this, and use <code>math</code> to create new dataframe columns from old ones? An explanation of why <code>math</code> isn't playing nice with the dataframe would be great too.</p>