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

We want to get the indices for the upper and lower triangles of a square matrix. Or in other words, where the identity matrix is zero

np.eye(len(df))

array([[ 1.,  0.,  0.],
       [ 0.,  1.,  0.],
       [ 0.,  0.,  1.]])

So I subtract it from 1 and

array([[ 0.,  1.,  1.],
       [ 1.,  0.,  1.],
       [ 1.,  1.,  0.]])

In a boolean context and passed to np.where I get exactly the upper and lower triangle indices.

i, j = np.where(1 - np.eye(len(df)))
df.iloc[i].reset_index(drop=True).join(
    df.iloc[j].reset_index(drop=True), rsuffix='_2')

   id value  id_2 value_2
0   1     a     2       b
1   1     a     3       c
2   2     b     1       a
3   2     b     3       c
4   3     c     1       a
5   3     c     2       b