熊貓系列.loc（）訪問錯誤後追加

Question

我有一個多指標熊貓系列如下。我想添加一個新條目（new_series）至multi_df，將其稱爲multi_df_appended。但是我不明白multi_df和multi_df_appended之間的行爲變化，當我嘗試訪問不存在的多索引時。

下面是重現問題的代碼。我想倒數第二行代碼：multi_df_appended.loc['five', 'black', 'hard', 'square' ]返回一個空的系列，就像它與multi_df一樣，但是我得到了給出的錯誤。我在這裏做錯了什麼？

df = pd.DataFrame({'id' : range(1,9), 
        'code' : ['one', 'one', 'two', 'three', 
           'two', 'three', 'one', 'two'], 
        'colour': ['black', 'white','white','white', 
          'black', 'black', 'white', 'white'], 
        'texture': ['soft', 'soft', 'hard','soft','hard', 
             'hard','hard','hard'], 
        'shape': ['round', 'triangular', 'triangular','triangular','square', 
             'triangular','round','triangular'] 
        }, columns= ['id','code','colour', 'texture', 'shape']) 
multi_df = df.set_index(['code','colour','texture','shape']).sort_index()['id'] 

# try to access a non-existing multi-index combination: 
multi_df.loc['five', 'black', 'hard', 'square' ] 
Series([], dtype: int64) # returns an empty Series as desired/expected. 

# append multi_df with a new row 
new_series = pd.Series([9], index = [('four', 'black', 'hard', 'round')]) 
multi_df_appended = multi_df.append(new_series) 

# now try again to access a non-existing multi-index combination: 
multi_df_appended.loc['five', 'black', 'hard', 'square' ] 
error: 'MultiIndex lexsort depth 0, key was length 4' # now instead of the empty Series, I get an error!? 

Answer 1

由於@Jeff回答，如果我做.sortlevel(0)，然後運行.loc()未知指數，它並沒有給「lexsort深度」錯誤：

multi_df_appended_sorted = multi_df.append(new_series).sortlevel(0) 
multi_df_appended_sorted.loc['five', 'black', 'hard', 'square' ] 
Series([], dtype: int64)