In [600]: A = df.query('letter == "A"').code.item()

In [601]: df.code.apply(lambda x: len(set(x).intersection(A))/float(len(A)))
Out[601]:
0    1.000000
1    0.333333
2    0.333333
Name: code, dtype: float64

In [602]: B = df.query('letter == "B"').code.item()

In [603]: df.code.apply(lambda x: len(set(x).intersection(B))/float(len(B)))
Out[603]:
0    0.5
1    1.0
2    1.0
Name: code, dtype: float64

In [604]: A
Out[604]: ['13.45', '16.59', '12.28']

In [605]: B
Out[605]: ['13.45', '18.20']