放大设置

The .loc/[] operations can perform enlargement when setting a non-existent key for that axis.

In the Series case this is effectively an appending operation.

  1. In [130]: se = pd.Series([1,2,3])
  3. In [131]: se
  4. Out[131]: 
  5. 0    1
  6. 1    2
  7. 2    3
  8. dtype: int64
  10. In [132]: se[5] = 5.
  12. In [133]: se
  13. Out[133]: 
  14. 0    1.0
  15. 1    2.0
  16. 2    3.0
  17. 5    5.0
  18. dtype: float64

A DataFrame can be enlarged on either axis via .loc.

  1. In [134]: dfi = pd.DataFrame(np.arange(6).reshape(3,2),
  2.    .....:                 columns=['A','B'])
  3.    .....: 
  5. In [135]: dfi
  6. Out[135]: 
  7.    A  B
  8. 0  0  1
  9. 1  2  3
  10. 2  4  5
  12. In [136]: dfi.loc[:,'C'] = dfi.loc[:,'A']
  14. In [137]: dfi
  15. Out[137]: 
  16.    A  B  C
  17. 0  0  1  0
  18. 1  2  3  2
  19. 2  4  5  4

This is like an append operation on the DataFrame.

  1. In [138]: dfi.loc[3] = 5
  3. In [139]: dfi
  4. Out[139]: 
  5.    A  B  C
  6. 0  0  1  0
  7. 1  2  3  2
  8. 2  4  5  4
  9. 3  5  5  5