title: How to select rows with NaN in particular column?
body: <p>Given this dataframe, how to select only those rows that have &quot;Col2&quot; equal to <code>NaN</code>?</p>
  <pre><code>df = pd.DataFrame([range(3), [0, np.NaN, 0], [0, 0, np.NaN], range(3), range(3)], columns=[&quot;Col1&quot;, &quot;Col2&quot;, &quot;Col3&quot;])
  </code></pre>
  <p>which looks like:</p>
  <pre><code>   0   1   2
  0  0   1   2
  1  0 NaN   0
  2  0   0 NaN
  3  0   1   2
  4  0   1   2
  </code></pre>
  <p>The result should be this one:</p>
  <pre><code>   0   1   2
  1  0 NaN   0
  </code></pre>