title: Unable to extract values from a list using pandas
body: <p>I have a data set which is something like below</p>
  
  <pre><code>data = [("patient 1", 0.44), ("patient 2", 0.14), ("patient 3", 0.22)]
  </code></pre>
  
  <p>So I need to create a list of first values of every tuple. So this is what I do</p>
  
  <pre><code>df = pd.DataFrame(np.array(data))
  values = df.iloc[:, 0].unique() 
  </code></pre>
  
  <p>So I get an expected list which looks like below</p>
  
  <pre><code>['patient 1', 'patient 2', 'patient 3']
  </code></pre>
  
  <p>But sometimes my dataset might have some missing values. So it maybe something like this</p>
  
  <pre><code>data = [("patient 1", 0.44), ("patient 2", 0.14), ("patient 3",)]
  </code></pre>
  
  <p>As you can see, the value for <code>patient 3</code> is empty or None. So when I run the above program again, instead of getting the list of first values of every tuple, I get the original list as it is</p>
  
  <pre><code>[('patient 1', 0.44), ('patient 2', 0.14), ('patient 3',)]
  </code></pre>
  
  <p>How do I ensure that despite the data being incomplete, I get the list I want since I only want the first values of each tuple?</p>
  
  <p><strong>Note:</strong> I know I can use simple python to extract first values but since the data set can be very big, I want to stick to <code>Pandas</code> to get the result.</p>