how to union two data frames so that every value in one data frame is linked to all values in another using python and pandas

Question

For example, the data is:

a=pd.DataFrame({'aa':[1,2,3]})
b=pd.DataFrame({'bb':[4,5]})

what I want is to union these two data frames so the new frame is :

aa    bb
1      4
1      5
2      4
2      5
3      4
3      5

You can see that every value in a is linked to all the values in b in the new frame. I probably can use tile or repeat to do this. But I have multiple frames which need to be done repeatedly. So I want to know if there is a better way?

Could anyone help me out here?

Answer 1

You can do it like this:

In [24]: a['key'] = 1

In [25]: b['key'] = 1

In [27]: pd.merge(a, b, on='key').drop('key', axis=1)
Out[27]: 
   aa  bb
0   1   4
1   1   5
2   2   4
3   2   5
4   3   4
5   3   5

Answer 2

you can use pd.MultiIndex.from_product and then reset_index. It is generating all the combinations between both set of data (the same idea than itertools.product)

df_outut = (pd.DataFrame(index=pd.MultiIndex.from_product([a.aa,b.bb],names=['aa','bb']))
              .reset_index())

and you get

   aa  bb
0   1   4
1   1   5
2   2   4
3   2   5
4   3   4
5   3   5