将两个大熊猫数据框与第一个索引相连吗？

Question

I have two dataframes, df1 :

    column1     column2
0   A           B
1   A           A
2   C           A
3   None        None
4   None        None

and df2

    id          l
40  100005090   A
188 100020985   B

Now I want to join df1 and df2 , but I don't know how to match the indices. If I simply do df1.join(df2) , the indices are aligned to df2 . That is, it finds the 40th entry of df2 and that is now the first entry of the dataframe that starts at 40 ( df1 ). How do I tell pandas to align indices to df1 , meaning that the first entry of df2 is actually index 40? That is, I would like to get:

    id          l    column1     column2
40  100005090   A          A           B
188 100020985   B          A           A
...

Answer 1

You can take a slice of your df that is the same length as df1 , then you can overwrite the index values and then join :

In [174]:    
sub = df.iloc[:len(df1)]
sub.index = df1.index
df1.join(sub)

Out[174]:
            id  l column1 column2
40   100005090  A       A       B
188  100020985  B       A       A

If the dfs are the same length then the first line is not needed, you just overwrite the index with the index values from the other df.