python - Indexing numpy array with another numpy array

Question

Suppose I have

a = array([[1, 2],
           [3, 4]])

and

b = array([1,1])

I'd like to use b in index a, that is to do a[b] and get 4 instead of [[3, 4], [3, 4]]

I can probably do

a[tuple(b)]

Is there a better way of doing it?

Thanks

Answer 1

According the numpy tutorial:

a[tuple(b)] 

is the correct way to do this:

http://www.scipy.org/Tentative_NumPy_Tutorial#head-3f4d28139e045a442f78c5218c379af64c2c8c9e

Answer 2

Suppose you want to access a subvector of a with n index pairs stored in blike so:

b = array([[0, 0],
       ...
       [1, 1]])

This can be done as follows:

a[b[:,0], b[:,1]]

For a single pair index vector this changes to a[b[0],b[1]], but I guess the tuple approach is easier to read and hence preferable.