我有一个多索引、多列的数据帧:
start A B C D
0 2019 35.156667 51.621111 18.858684 1
1 2019 NaN 50.211905 18.991290 -1
2 2019 42.836250 58.778235 18.788889 1
3 2020 NaN 8.188000 17.805833 1
4 2020 42.568000 55.907143 17.300000 -1
5 2021 46.458333 42.293750 26.322500 1
6 2021 43.675000 60.475000 29.520000 1
每年("开始"列(,如果D>0,我想用正向值填充a列中的NaN,如果D<0:
start A B C D
0 2019 35.156667 51.621111 18.858684 1
1 2019 35.156667 50.211905 18.991290 -1
2 2019 42.836250 58.778235 18.788889 1
3 2020 42.568000 8.188000 17.805833 1
4 2020 42.568000 55.907143 17.300000 -1
5 2021 46.458333 42.293750 26.322500 1
6 2021 43.675000 60.475000 29.520000 1
我在尝试:
df[['A','D']] = df.groupby('start').apply(lambda x: x['A'].fillna(method='ffill') if x['D']>0 else x['A'].fillna(method='bfill'))
但我会遇到这样的错误:
The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().
有什么帮助吗?谢谢
使用按组向前和向后填充的GroupBy.agg
,然后通过numpy.where
:设置值
df1 = df.groupby('start')['A'].agg(['ffill','bfill'])
print (df1)
ffill bfill
0 35.156667 35.156667
1 35.156667 42.836250
2 42.836250 42.836250
3 NaN 42.568000
4 42.568000 42.568000
5 46.458333 46.458333
6 43.675000 43.675000
print (df1.columns)
Index(['ffill', 'bfill'], dtype='object')
df['A'] = np.where(df['D'] < 0, df1['ffill'], df1['bfill'])
print (df)
start A B C D
0 2019 35.156667 51.621111 18.858684 1
1 2019 35.156667 50.211905 18.991290 -1
2 2019 42.836250 58.778235 18.788889 1
3 2020 42.568000 8.188000 17.805833 1
4 2020 42.568000 55.907143 17.300000 -1
5 2021 46.458333 42.293750 26.322500 1
6 2021 43.675000 60.475000 29.520000 1
同样,如果每组只有2个值,则不需要检查D
(取决于数据(:
df['A'] = df.groupby('start')['A'].apply(lambda x: x.ffill().bfill())
print (df)
start A B C D
0 2019 35.156667 51.621111 18.858684 1
1 2019 35.156667 50.211905 18.991290 -1
2 2019 42.836250 58.778235 18.788889 1
3 2020 42.568000 8.188000 17.805833 1
4 2020 42.568000 55.907143 17.300000 -1
5 2021 46.458333 42.293750 26.322500 1
6 2021 43.675000 60.475000 29.520000 1