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python - 将一个数据框中的行替换为另一个

问题描述

我正在尝试将一个数据框中的行的值替换为另一个。

以下是示例代码

import pandas as pd
import numpy as np
from pprint import pprint

raceA = ['r1','r3','r4','r5','r6','r7','r8', 'r9']
qualifierA = ['last','first','first','first','last','last','first','first']
participantA = ['rat','rat','cat','cat','rat','dog','dog','dog']
dfA = pd.DataFrame(
    {'race':raceA,
     'qualifier':qualifierA,
     'participant':participantA

    }
)
pprint(dfA)

raceB = ['r1','r2','r3','r4','r5','r6','r7','r8', 'r9','r10']
qualifierB = ['last',np.nan,np.nan,'first','first','last','last','first','first',np.nan]
participantB = ['rat','rat',np.nan,'cat','cat','rat','dog','dog',np.nan,np.nan]
dfB = pd.DataFrame(
    {'race':raceB,
     'qualifier':qualifierB,
     'participant':participantB

    }
)
pprint(dfB)
dfB.loc[dfB.race.isin(dfA.race), ['qualifier','participant']] = dfA[['qualifier','participant']]
pprint(dfB)

例如在 dfA 中，

r9     first         dog

dfB 包含，

 r9     first         NaN

所需输出：dfB

r9     first         dog

获得的输出：

r9       NaN         NaN

有人可以调查一下吗？

标签： pythonpython-3.xpandasdataframe

解决方案

与数据框一起使用DataFrame.fillna：

df = dfB.set_index('race').fillna(dfA.set_index('race')).reset_index()

print(df)
  race qualifier participant
0   r1      last         rat
1   r2       NaN         rat
2   r3     first         rat
3   r4     first         cat
4   r5     first         cat
5   r6      last         rat
6   r7      last         dog
7   r8     first         dog
8   r9     first         dog
9  r10       NaN         NaN

或使用update：

dfB = dfB.set_index('race')
dfA = dfA.set_index('race')

dfB.update(dfA)

print(dfB.reset_index())
 race qualifier participant
0   r1      last         rat
1   r2       NaN         rat
2   r3     first         rat
3   r4     first         cat
4   r5     first         cat
5   r6      last         rat
6   r7      last         dog
7   r8     first         dog
8   r9     first         dog
9  r10       NaN         NaN

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