title: Can't drop pandas column
body: <p>I have a pandas dataframe that I need to slice into several tables based on values and save into several .csv files. This method seems to work, however it creates a column (first one) that I cannot drop (instead drops 2nd column). Could someone tell me why it is there and how can I get rid of it? Thank you. Here is the code:</p>
  
  <pre><code>new_d['Supplier'] = new_d.apply(lambda row: determine_supplier(row), axis = 1)
  new_d.sort_values(by = ['Supplier'], inplace = True)
  new_d.set_index(keys = ['Supplier'], drop = False, inplace = True)
  suppliers = new_d['Supplier'].unique().tolist()
  for supplier in suppliers:
    po = new_d.loc[new_d.Supplier == supplier] #the problem is here?
    po = po.drop(po.columns[[0]], axis = 1) # can't drop
    po.to_csv(path_or_buf = r'PO\\' + supplier + '_PO.csv')
  </code></pre>