[英]Pandas (Python) - Update column of a dataframe from another one with conditions
I had a problem and I found a solution but I feel it's the wrong way to do it. 我有一个问题,我找到了一个解决方案,但我觉得这是错误的方法。 Maybe, there is a more 'canonical' way to do it. 也许,有一种更“规范”的方式来做到这一点。
Problem 问题
I have two dataframe that I would like to merge without having extra column and without erasing existing infos. 我有两个数据框,我想合并,没有额外的列,也没有删除现有的信息。 Example : 示例:
Existing dataframe (df) 现有数据帧(df)
A A2 B
0 1 4 0
1 2 5 1
Dataframe to merge (df2) 要合并的数据帧(df2)
A A2 B
0 1 4 2
1 3 5 2
I would like to update df
with df2
if columns 'A' and 'A2' corresponds. 如果列'A'和'A2'对应,我想用df2
更新df
。 The result would be (: 结果将是(:
A A2 B
0 1 4 2.0 <= Update value ONLY
1 2 5 1.0
Here is my solution, but I think it's not a really good one. 这是我的解决方案,但我认为这不是一个非常好的解决方案。
import pandas as pd
df = pd.DataFrame([[1,4,0],[2,5,1]],columns=['A','A2','B'])
df2 = pd.DataFrame([[1,4,2],[3,5,2]],columns=['A','A2','B'])
df = df.merge(df2,on=['A', 'A2'],how='left')
df['B_y'].fillna(0, inplace=True)
df['B'] = df['B_x']+df['B_y']
df = df.drop(['B_x','B_y'], axis=1)
print(df)
Does anyone has a better way to do ? 有没有人有更好的方法呢? Thanks ! 谢谢 !
Yes, it can be done without merge: 是的,它可以在没有合并的情况下完成:
rows = (df[['A','A2']] == df2[['A','A2']]).all(axis=1)
df.loc[rows,'B'] = df2.loc[rows,'B']
You can try this: 你可以试试这个:
df.ix[df2.loc[(df['A'] == df2['A']) & (df['A2'] ==
df2['A2']),'B'].index.values,'B'] = \
df2.loc[(df['A'] == df2['A']) & (df['A2'] == df2['A2']),'B']
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