title: Extract dictionary value from column in data frame
body: <p>I'm looking for a way to optimize my code. </p>
  
  <p>I have entry data in this form:</p>
  
  <pre><code>import pandas as pn
  
  a=[{'Feature1': 'aa1','Feature2': 'bb1','Feature3': 'cc2' },
   {'Feature1': 'aa2','Feature2': 'bb2' },
   {'Feature1': 'aa1','Feature2': 'cc1' }
   ]
  b=['num1','num2','num3']
  
  
  df= pn.DataFrame({'num':b, 'dic':a })
  </code></pre>
  
  <p>I would like to extract element 'Feature3' from dictionaries in column 'dic'(if exist) in above data frame. So far I was able to solve it but I don't know if this is the fastest way, it seems to be a little bit over complicated.</p>
  
  <pre><code>Feature3=[]
  for idx, row in df['dic'].iteritems():
      l=row.keys()
  
      if 'Feature3' in l:
          Feature3.append(row['Feature3'])
      else:
          Feature3.append(None)
  
  df['Feature3']=Feature3
  print df
  </code></pre>
  
  <p>Is there a better/faster/simpler way do extract this Feature3 to separate column in the dataframe?</p>
  
  <p>Thank you in advance for help.</p>