how to append every row of pandas dataframe to every row of another dataframe

Question

for example, df1 is a 3*2 dataframe, and df2 is a 10*3 dataframe, what I want is to generate a new dataframe of 30*5, where each row in df1 is appended with the 3 columns of df2 for all 10 rows in df2.

I know I can use iteration to append columns of df2 to each row of df1, but I am wondering whether there are some more efficient way to do this in pandas, like its concat functions.

could anyone help?

regards, nan

Answer 1

If I understand you, you need cartesian product. You can emulate this with merge in pandas:

>>> df1 = pd.DataFrame({'A':list('abc'), 'B':range(3)})
>>> df2 = pd.DataFrame({'C':list('defg'), 'D':range(3,7)})
>>> df1['key'] = 1
>>> df2['key'] = 1
>>> df = pd.merge(df1, df2, on='key')
>>> del df['key']
>>> df
    A  B  C  D
0   a  0  d  3
1   a  0  e  4
2   a  0  f  5
3   a  0  g  6
4   b  1  d  3
5   b  1  e  4
6   b  1  f  5
7   b  1  g  6
8   c  2  d  3
9   c  2  e  4
10  c  2  f  5
11  c  2  g  6