Bought Together in Python

"Customers who bought this also bought…" starts with one count: for each pair of products, how many customers bought both. With the last lesson's 0/1 customer by product table, one line counts every pair at once.

Turn and multiply: matrix.T gives back the table turned on its side, with one row per product and one column per customer. @ multiplies two tables: each cell of the result is a row of the left one times a column of the right one, cell by cell, added up. Since 1 × 1 is 1 and anything × 0 is 0, one product's row times another product's column counts the customers with a 1 in both. Here is a small example with 3 customers and 2 products:

a = np.array([[1, 0], [1, 1], [0, 1]])
print(a.T @ a)
# [[2 1]
#  [1 2]]

The result has one row and one column per product, and it is a mirror: row A, column B equals row B, column A. On the diagonal, a product meets itself, which gives its number of buyers. To read one product's partners, take its column and .drop() its own row: drop(label) gives back the Series without that label. Then sort_values(ascending=False) and head(3) give the top 3.

Your program must print:

product    Gift card  Lamp  Mug  Notebook  Pen  Plant  Stapler  Teapot
product
Gift card        197    90   76        59   67     79       58      76
Lamp              90   116   36        30   29     71       31      35
Mug               76    36  103        27   29     36       23      64
Notebook          59    30   27        96   49     27       52      30
Pen               67    29   29        49   98     25       48      30
Plant             79    71   36        27   25    111       24      28
Stapler           58    31   23        52   48     24       92      26
Teapot            76    35   64        30   30     28       26     107
product
Gift card    76
Mug          64
Lamp         35

Your task: matrix is already made. Count the customers of every pair of products in together and print it. Then put the Teapot's column, without the Teapot itself, in with_teapot, sort it from the largest count down and print its first 3.

Assignment
Follow the Coding Tutorial to count the products bought together and find the 3 bought most often with the Teapot.

Hint
Turn the left table, not the right one: products must end up on both sides. Without .drop("Teapot"), the Teapot comes first in its own list, with 107.