pandas DataFrame 索引(二)

    构造DataFrame

from pandas import Series,DataFrame

import numpy as np

frame=DataFrame(np.arange(9).reshape((3,3)),index=['a','c','d'],columns=['ohio','texas','california'])

frame
Out[73]: 
   ohio  texas  california
a     0      1           2
c     3      4           5
d     6      7           8

    按照索引提取

frame2=frame.reindex(['a','b','c','d'])

frame2
Out[75]: 
   ohio  texas  california
a   0.0    1.0         2.0
b   NaN    NaN         NaN
c   3.0    4.0         5.0
d   6.0    7.0         8.0

    按照columns 提取

states=['texas','utah','california']
frame.reindex(columns=states)

Out[76]: 
   texas  utah  california
a      1   NaN           2
c      4   NaN           5
d      7   NaN           8

    按照索引和columns提取

states=['texas','utah','california']
frame.reindex(index=['a','b','c','d'],method='ffill',columns=states)

Out[77]: 
   texas  utah  california
a      1   NaN           2
b      1   NaN           2
c      4   NaN           5
d      7   NaN           8

    简便方法

frame.ix[['a','b','c','d'],states]
Out[79]: 
   texas  utah  california
a    1.0   NaN         2.0
b    NaN   NaN         NaN
c    4.0   NaN         5.0
d    7.0   NaN         8.0
posted @ 2022-08-19 23:00  luoganttcc  阅读(19)  评论(0编辑  收藏  举报