title: Pandas mapping to TRUE/FALSE as String, not Boolean
body: <p>When I try to convert some columns in a pandas dataframe from '0' and '1' to 'TRUE' and 'FALSE', pandas automatically detects dtype as boolean. I want to keep dtype as string, with the strings 'TRUE' and 'FALSE'.</p>
  
  <p>See code below:</p>
  
  <pre><code>booleanColumns = pandasDF.select_dtypes(include=[bool]).columns.values.tolist()
  booleanDictionary = {'1': 'TRUE', '0': 'FALSE'}
  
  pandasDF.to_string(columns = booleanColumns)
  
  for column in booleanColumns:
      pandasDF[column].map(booleanDictionary)
  </code></pre>
  
  <p>Unfortunately, python automatically converts dtype to boolean with the last operation. How can I prevent this?</p>