How to Calculate the Cartesian Product of Two Pandas DataFrames?

Cartesian Product in Pandas

Problem:

Obtain the Cartesian product of two Pandas dataframes without explicitly defining it.

Example:

import pandas as pd

df1 = pd.DataFrame({'col1': [1, 2], 'col2': [3, 4]})
df2 = pd.DataFrame({'col3': [5, 6]})

Desired output:

   col1  col2  col3
0     1     3     5
1     1     3     6
2     2     4     5
3     2     4     6

Solution:

For Pandas >= 1.2:

Using the built-in merge function:

df1.merge(df2, how='cross')

For Pandas

Using merge with a repeated key:

key_df = pd.DataFrame({'key': [1, 1], 'col1': [1, 2], 'col2': [3, 4]})
merge(key_df, df2, on='key')[['col1', 'col2', 'col3']]

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