title: 'function' object has no attribute 'columns'
body: <p>I tried to encode columns as categories.</p>
  
  <p>I can not work on my data frame because all columns are dtypes: object.</p>
  
  <p>My code is:</p>
  
  <p>categorize_column = lambda x: x.astype('category')</p>
  
  <p>df.columns = df.columns.apply(categorize_column, axis=0)</p>
  
  <p>I get an error:</p>
  
  <p>'function' object has no attribute 'columns'</p>