用另一个数据帧中的数据替换一个数据帧中的数据

Question

I have two data-frames where df1 looks like:

id  Status Colour 
 1      On   Blue
19      On    Red
 4      On  Green
56      On   Blue

df2 looks like

id   Status
19      Off
 4     Even

I am trying to replace the Status in df1 with the Status in df2 if the id is present in both data-frames so my resulting data-frame looks like:

id  Status  Colour 
 1      On    Blue
19     Off     Red
 4    Even   Green
56      On    Blue 

I can identify the field in df1 that I want to change using:

df1.loc[df1['id'].isin(df2['id']), 'Status'] = referenced date

But I can't see how to identify the field in df2 to pass to df1 (the part to the right of the above equals sign)

How can I do this?

Answer 1

Use Series.map with replace non matched missing values by fillna :

df1['Status'] = df1['id'].map(df2.set_index('id')['Status']).fillna(df1['Status'])
print (df1)
   id Status Colour
0   1     On   Blue
1  19    Off    Red
2   4   Even  Green
3  56     On   Blue

Answer 2

try like below

result = df1.merge(df2, on='id', how='left')
result['status'] = result['status_y'].fillna(result['status_x'])
result.drop(['status_x','status_y'],axis=1,inplace=True)


   color  id status
0   blue   1     on
1    red  19    off
2  green   4   even
3   blue  56     on