Question

我正在使用pandas（版本0.20.3）并且我希望将diff方法应用于groupby，而不是DataFrame，结果是＆＃34;下划线＆＃34;。

以下是代码：

import numpy as np
import pandas as pd

# creating the DataFrame
data = np.random.random(18).reshape(6,3)
indexes = ['B']*3 + ['A']*3
columns = ['x', 'y', 'z']
df = pd.DataFrame(data, index=indexes, columns=columns)
df.index.name = 'chain_id'

# Now I want to apply the diff method in function of the chain_id
df.groupby('chain_id').diff()

结果是下划线！请注意，df.loc [＆＃39; A＆＃39;]。diff（）和df.loc [＆＃39; B＆＃39;]。diff（）返回预期的结果，所以我不明白为什么它不会与groupby合作。

Answer 1

IIUC，您的错误：无法从重复的轴重新索引

df.reset_index().groupby('chain_id').diff().set_index(df.index)
Out[859]: 
                 x         y         z
chain_id                              
B              NaN       NaN       NaN
B        -0.468771  0.192558 -0.443570
B         0.323697  0.288441  0.441060
A              NaN       NaN       NaN
A        -0.198785  0.056766  0.081513
A         0.138780  0.563841  0.635097

pandas：使用diff with groupby

1 个答案: