Cartesian product of a pandas dataframe with itself

Question

Given a dataframe:

    id  value
0    1     a
1    2     b
2    3     c

I want to get a new dataframe that is basically the cartesian produ

Answer 1

This can be done entirely in pandas:

df.loc[:, 'key_col'] = 1 # create a join column that will give us the Cartesian Product

(df.merge(df, df, on='key_col', suffixes=('', '_2'))
 .query('id != id_2') # filter out joins on the same row
 .drop('key_col', axis=1)
 .reset_index(drop=True))

Or if you don't want to have to drop the dummy column, you can temporarily create it when calling df.merge:

(df.merge(df, on=df.assign(key_col=1)['key_col'], suffixes=('', '_2'))
 .query('id != id_2') # filter out joins on the same row
 .reset_index(drop=True))