title: Calculating sin over a column with missing values
body: <p>I have a pandas DataFrame with columns of 2 geo locations (long_1, lat_1, long_2, lat_2) and I want to add a column for the distance between them. The approximated formula can be found in the internet, ignore the details, it involves sin and cos and that's where my problem is.</p>
  
  <p>I want to calculate <code>np.sin( df["long_1"] )</code>. It works if all values are not null but once I have missing values it throws an error instead of returning <code>NaN</code>. I get the following error:</p>
  
  <pre><code>In [97]: np.sin( df["long_1"] )
  ---------------------------------------------------------------------------
  AttributeError                            Traceback (most recent call last)
  &lt;ipython-input-97-d95dd98ecd44&gt; in &lt;module&gt;()
  ----&gt; 1 np.sin( df["long_1"] )
  
  AttributeError: sin
  </code></pre>
  
  <p>Any idea what might be the problem? Or if I'm wrong here - what's the best way to calculate sin/cos over a Series with some missing values (expected behaviour should be to return <code>NaN</code> when the input value is missing).</p>
  
  <p>Thanks!</p>