Classifying an array

Question

For instance I have this list:

A = [(1, 2.5), (2, 5.0), (3, 7.5), (4, 10.0)]

and I have another list with the following entry:

B = [2.5, 7.5, 12.5]

What I want is a program in Python where if the 2nd element of each tuple in A , namely 2.5 , 5.0 , 7.5 , and 10.0 , can be found in B , it will create another variable which looks like this:

C = [(1, 2.5), (3, 7.5)]

where it removes the other tuples in A whose 2nd elements are not in B . I tried to code it this way:

A = [(1, 2.5), (2, 5.0), (3, 7.5), (4, 10.0)]
D = np.asarray(list(A))
E = []
if D[:, 1] in B:
    E = np.append(E,D)
else:
    pass

but I got an error of:

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Answer 1

Why not simply the following:

>>> A = [(1,2.5), (2,5.0), (3,7.5), (4,10.0)]
>>> B = [2.5, 7,5, 12.5]
>>> C = [a for a in A if a[1] in B]
>>> C
[(1, 2.5), (3, 7.5)]

Answer 2

You could use np.n1d to determine which values in A[:, 1] are also in B :

In [104]: A = np.array([(1,2.5), (2,5.0), (3,7.5), (4,10.0)])

In [105]: B = [2.5, 7.5, 12.5]

In [106]: mask = np.in1d(A[:, 1], B)

In [107]: mask
Out[107]: array([ True, False,  True, False], dtype=bool)

In [108]: A[mask]
Out[108]: 
array([[ 1. ,  2.5],
       [ 3. ,  7.5]])