Pandas: How To Convert A List Into A Matrix Grouped By A Column?

I have a pandas dataframe where the first column (CUSTOMER) is the name of the customer and the customer's name is repeated once for every product the customer has purchased (PRODU

Solution 1:

Self merge with crosstab

d1 = df.merge(df, on='Customer').query('Product_x != Product_y')
pd.crosstab(d1.Product_x, d1.Product_y)

Product_y  A  B  C
Product_x         
A          0  2  1
B          2  0  1
C          1  1  0

---

You can see this answer to get a better idea how to speed the crosstab up. The key insight for this problem was the self merging.