使用dataframes列以相同顺序从另一个框架中选择行

Question

Need some pandas jump start here:

Consider two data frames A and B . Both contain a column id with identifier values:

A: id     valA
   8      ?
   2      ?
   4      ?

B: id     valB    valC   
   1      ?       ?      
   4      ?       ?      
   3      ?       ?      
   8      ?       ?      
   2      ?       ?      

I need a version of dataframe B which contains only the rows that contain the identifiers from A[id] , in exactly the same order as in A . That is:

B': id     valB     valC
    8      ?        ?
    2      ?        ?
    4      ?        ?

I assume this is a basic operation in pandas, but it seems I am missing the vocabulary to google it right now.

I've tried

B.loc[B['id'].isin(A['id'])]

but that doesn't seem to be the solution - the column id in the result doesn't have the same order of values as in A .

Answer 1

You could use pd.merge

In [92]: A.merge(B)
Out[92]:
   id valA valB valC
0   8    ?    ?    ?
1   2    ?    ?    ?
2   4    ?    ?    ?