title: Checking if particular value (in cell) is NaN in pandas DataFrame not working using ix or iloc
body: <p>Lets say I have following <code>pandas</code> <code>DataFrame</code>:</p>
  
  <pre><code>import pandas as pd
  df = pd.DataFrame({"A":[1,pd.np.nan,2], "B":[5,6,0]})
  </code></pre>
  
  <p>Which would look like:</p>
  
  <pre><code>&gt;&gt;&gt; df
       A  B
  0  1.0  5
  1  NaN  6
  2  2.0  0
  </code></pre>
  
  <h2>First option</h2>
  
  <p>I know one way to check if a particular value is <code>NaN</code>, which is as follows:</p>
  
  <pre><code>&gt;&gt;&gt; df.isnull().ix[1,0]
  True
  </code></pre>
  
  <h2>Second option (not working)</h2>
  
  <p>I thought below option, using <code>ix</code>, would work as well, but it's not:</p>
  
  <pre><code>&gt;&gt;&gt; df.ix[1,0]==pd.np.nan
  False
  </code></pre>
  
  <p>I also tried <code>iloc</code> with same results:</p>
  
  <pre><code>&gt;&gt;&gt; df.iloc[1,0]==pd.np.nan
  False
  </code></pre>
  
  <p>However if I check for those values using <code>ix</code> or <code>iloc</code> I get:</p>
  
  <pre><code>&gt;&gt;&gt; df.ix[1,0]
  nan
  &gt;&gt;&gt; df.iloc[1,0]
  nan
  </code></pre>
  
  <p>So, <strong>why is the second option not working?</strong> Is it possible to check for <code>NaN</code> values using <code>ix</code> or <code>iloc</code>?</p>