如何在从具有相同索引的第一个数据帧中删除行时合并pandas数据帧？

Question

假设我有2个数据帧，df1和df2

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假设他们的索引是subject_id，我该如何获得以下内容：

subject_id first_name last_name        
1                Alex  Anderson
2                 Amy  Ackerman
3               Allen       Ali
4               Alice      Aoni
5              Ayoung   Atiches

subject_id first_name last_name
4               Billy    Bonder
5               Brian     Black
6                Bran   Balwner
7               Bryce     Brice
8               Betty    Btisan

当我在这时，如何得到这个：

subject_id first_name last_name        
1                Alex  Anderson
2                 Amy  Ackerman
3               Allen       Ali
4               Billy    Bonder
5               Brian     Black
6                Bran   Balwner
7               Bryce     Brice
8               Betty    Btisan

Answer 1

使用combine_first，如有必要，请先使用set_index：

df11 = df1.set_index('subject_id')
df22 = df2.set_index('subject_id')

df3 = df22.combine_first(df11).reset_index()
print (df3)
   subject_id first_name last_name
0           1       Alex  Anderson
1           2        Amy  Ackerman
2           3      Allen       Ali
3           4      Billy    Bonder
4           5      Brian     Black
5           6       Bran   Balwner
6           7      Bryce     Brice
7           8      Betty    Btisan

df3 = df11.combine_first(df22).reset_index()
print (df3)
   subject_id first_name last_name
0           1       Alex  Anderson
1           2        Amy  Ackerman
2           3      Allen       Ali
3           4      Alice      Aoni
4           5     Ayoung   Atiches
5           6       Bran   Balwner
6           7      Bryce     Brice
7           8      Betty    Btisan

Answer 2

我们可以使用pd.concat和drop_duplicates，（抱歉似乎是这样，隐藏他们的格式......，这会让答案难看......）

pd.concat([df1,df2]).drop_duplicates('subject_id',keep='first')

Out[95]: subject_id first_name last_name 0 1 Alex Anderson 1 2 Amy Ackerman 2 3 Allen Ali 3 4 Alice Aoni 4 5 Ayoung Atiches 2 6 Bran Balwner 3 7 Bryce Brice 4 8 Betty Btisan pd.concat([df1,df2]).drop_duplicates('subject_id',keep='last')

Out[96]: subject_id first_name last_name 0 1 Alex Anderson 1 2 Amy Ackerman 2 3 Allen Ali 0 4 Billy Bonder 1 5 Brian Black 2 6 Bran Balwner 3 7 Bryce Brice 4 8 Betty Btisan