如何将列值从一个 dataframe 提取到另一个？

Question

I have two pandas data frames df1 and df2

   **df1**                                **df2**  
cat  id  frequency            id   (other cols)    A    B    C
A    23    2                  23   .............  nan  nan  nan
A    43    8                  43   .............  nan  nan  nan
B    23    56                 30   .............  nan  nan  nan
C    30    4

I am looking for a way on how to extract information form df1 to df2 resulting in the format below, where the values of columns A, B and C are the frequency values from df1

       **df2**
id  (other cols)  A  B   C 
30   ..........   0  0   4
23   ..........   2  56  0
43   ..........   8  0   0

Answer 1

Use DataFrame.pivot with DataFrame.combine_first :

df11 = df1.pivot('cat', 'id', 'frequency')

#if id is column
df = df2.set_index('id').combine_first(df11)

#if id is index
df = df2.combine_first(df11)