Count ID's by using field values in python [duplicate]

Answer 1

You can do that with a simple matrix product:

import pandas as pd

df = pd.DataFrame({
    'Brand1': [1, 1, 1, 1, 1],
    'Brand2': [0, 0, 0, 1, 1],
    'Brand3': [0, 1, 1, 0, 0],
    'Brand4': [1, 0, 0, 0, 1],
})
cross = df.T @ df
print(cross)
#         Brand1  Brand2  Brand3  Brand4
# Brand1       5       2       2       2
# Brand2       2       2       0       1
# Brand3       2       0       2       0
# Brand4       2       1       0       2