Python: counting the number of combinations dataframe

what is an easy way to count the number of combinations in across two columns? Given this dataframe:

df =
id testA testB
1  3     NA
1  1     3
2  2     NA
2  NA    1
2  0     0
3  NA    NA
3  1     1

I would like to know the different combinations independently of the score. For example:

Both tests: 3
A but not B: 2
B but not A: 1

>Solution :

For two columns, can query each condition separately:

a_exists = df["testA"].notna()
b_exists = df["testB"].notna()

# both
>>> (a_exists & b_exists).sum()
3

# A, but not B
>>> (a_exists & ~b_exists).sum()
2

# B, but not A
>>> (~a_exists & b_exists).sum()
1

But can be automated with some itertools:

from itertools import compress, repeat

cols = ["A", "B"]
for ma, mb in product([0, 1], repeat=2):
    if ma == mb == 1: continue
    ab_info =  "".join(compress(cols, (1 - ma, 1 - mb)))
    counts  = ((a_exists ^ ma) & (b_exists ^ mb)).sum()

    print(ab_info, counts)

• get "selector"s over [0, 1] x 2
• if both are 1s, i.e., neither doesn’t exist, skip the selector
• otherwise
  • get the selected parties with compress
  • see whether to negate or not through bitwise XOR and AND the results
  • sum to get the total count

which prints

AB 3
A 2
B 1