当两个值在同一个groupby列pandas中时，如何创建一个矩阵？

Question

So i basically have a dataframe of products and orders:

product    order
 apple      111
 orange     111
 apple      121
 beans      121
 rice       131
 orange     131
 apple      141
 orange     141

What i need to do is, groupby the products based on the id of the order, and generate this matrix with the value of times they appeared together in the same order. I don't know any efficient way of doing this, if someone could help me!

           apple   orange  beans rice
 apple       x        2      1     0
 orange      2        x      0     1
 beans       1        0      x     0
 rice        0        1      0     x

Answer 1

One option is to join the dataframe with itself on order and then calculate the cooccurrences using crosstab on the two product columns:

df.merge(df, on='order').pipe(lambda df: pd.crosstab(df.product_x, df.product_y))

product_y  apple  beans  orange  rice
product_x                            
apple          3      1       2     0
beans          1      1       0     0
orange         2      0       3     1
rice           0      0       1     1

Answer 2

Another way is to perform a crosstab between product and order, then do a matrix multiplication @ with the transpose so:

a_ = pd.crosstab(df['product'], df['order'])
res = a_@a_.T
print(res)
product  apple  beans  orange  rice
product                            
apple        3      1       2     0
beans        1      1       0     0
orange       2      0       3     1
rice         0      0       1     1

or using pipe to do a one liner:

res = pd.crosstab(df['product'], df['order']).pipe(lambda x: x@x.T)