title: Trying to remove nan from csv file in python pandas
body: <p>I am trying to remove nan values from a final csv file, which will source data for digital signage.</p>
  
  <p>I use fillna to remove empty data to keep 'nan' from appearing on the sign. fillna is working, but because this data is formatted, I get <code>()-</code> in the empty csv fields.</p>
  
  <pre><code>df = pd.read_csv(filename)
      df = df.fillna('') 
      df = df.astype(str)
      df['PhoneNumber']=df['CONTACT PHONE NUMBER'].apply(lambda x: '('+x[:3]+')'+x[3:6]+'-'+x[6:10])
  </code></pre>
  
  <p>I tried writing an <code>if...else</code> statement to separate lines in the array; but since the formatting is applied to the entire list, not entry by entry, that doesn't work. </p>