cartesian product in pandas

Question

I have two pandas dataframes:

from pandas import DataFrame
df1 = DataFrame({\'col1\':[1,2],\'col2\':[3,4]})
df2 = DataFrame({\'col3\':[5,6]})     
         


        

Answer 1

You could start by taking the Cartesian product of df1.col1 and df2.col3, then merge back to df1 to get col2.

Here's a general Cartesian product function which takes a dictionary of lists:

def cartesian_product(d):
    index = pd.MultiIndex.from_product(d.values(), names=d.keys())
    return pd.DataFrame(index=index).reset_index()

Apply as:

res = cartesian_product({'col1': df1.col1, 'col3': df2.col3})
pd.merge(res, df1, on='col1')
#  col1 col3 col2
# 0   1    5    3
# 1   1    6    3
# 2   2    5    4
# 3   2    6    4