Extracting rows in a data frame based on multiple criteria?

Question

I have two data frames consisting multiple identical rows and similar columns as follows:

     mydf1:
           id, f1, f2 ,f3 , ..., fn
           x1, 34, 45 ,32 , ...,  0
           x1, 24, 55 ,1  , ...,  0
           x1, 67, 43 ,5  , ...,  0
           x2, 20, 89 ,4  , ...,  1
           x2, 24, 50 ,1  , ...,  1
           x3, 14, 15 ,1  , ...,  1
           x3, 44, 25 ,11  , ..., 1
           ..  ..  ..  ..    ... ..

      mydaf2:
             id, v1, v2 ,v3 , ...,vm
             x1, 74, 4 ,32 , ..., 32
             x2, 64, 5 ,10  , ..., 56
             x3, 4, 3 ,50  , ..., 78

Now, I want to create a new mydf_new consisting mydf2 and one extra column 'fn' taking from mydf1. As it can be seen from mydf1, fn is a feature that contains only 1 and 0 and it is identical for every id. For example, for x1, fn always is 0, for x2, fn always is 1 and so on. I want to add those 0 and 1 in the new data frame for the corresponding id, so my desired new data frame should be like this:

       mydaf_new:
             id, v1, v2, v3 , ..., vm, fn
             x1, 74, 4 , 32 , ..., 32, 0
             x2, 64, 5 , 10 , ..., 56, 1
             x3, 4,  3 , 50 , ..., 78, 1

Any idea that I fix this problem?

Answer 1

Try this:

df = mydf1[['id', 'fn']]
mydf_new = mydf2.merge(df, how='left', on='id')