title: using python pandas i want to normalize data frame column on non null values
body: <p>I have one data frame and i am reading that with pandas python , in that one column contains dictonay values and i want to normalize that column i.e i want to split and i am using this:</p>
  
  <pre><code>if 'X' in df_cols:
      def only_dict(d):
      '''
      Convert json string representation of dictionary to a 
  python dict
  '''
  return d
  
  A = json_normalize(df['X'].apply(only_dict).tolist()).add_prefix('X.')
  df = df.drop('X', axis=1).join(A)
  </code></pre>
  
  <p>but this column contains some null values too, so i want to apply only on column which have not null values using labmda is anyone have idea how to do it?</p>