pandas的pivot_table保留索引

我有一个数据框：

import pandas as pd

data = {'day_bucket': ['2011-01-21', '2011-01-22', '2011-01-23', '2011-01-24'], 'label': ['birds', 'birds', 'birds', 'birds'], 'numeric_value': [4, 0, 7, 3]}

df = pd.DataFrame(data)

   day_bucket  label  numeric_value
0  2011-01-21  birds              4
1  2011-01-22  birds              0
2  2011-01-23  birds              7
3  2011-01-24  birds              3

我想旋转这个数据框，以便我有一列birds及其下方的值。

pd.pivot_table(df, values='numeric_value', index='day_bucket',columns='label')  

gives:

label       birds
day_bucket             
2011-01-21  4
2011-01-22  0
2011-01-23  7
2011-01-24  3

我应该做什么来保留索引？结果将如下所示：

    day_bucket birds    
0   2011-01-21  4
1   2011-01-22  0
2   2011-01-23  7
3   2011-01-24  3 

set_index with append

df.set_index(['day_bucket', 'label'], append=True) \
  .rename_axis([None, None, None]).squeeze().unstack()


              birds
0 2011-01-21      4
1 2011-01-22      0
2 2011-01-23      7
3 2011-01-24      3