array indexing question

[Nick C]

I'm fairly new to this, so apologies in advance.  

Let's say I have a 3-d array A[i,j,k] of shape (Ni,Nj,Nk), and a list of labels I[k], where I[k] belongs to 0...Ni-1.

I want to create a new, 2-d array B[j,k] = A[I[k], j, k].

I've found one solution to this, which is:

ind_i = np.tile(I, (1,Nj)).T

ind_j = np.tile(np.arange(Nj), (1,Nk))

ind_k = np.tile(np.arange(Nk), (1, Nj)).T

B = A[ind_i, ind_j, ind_k]

but something seems...not ideal about this.  Can someone tell me if there's a simpler, better way?

Thanks,

Nick

[Nick C]

Ok, I think I found an improvement, myself; actually, it is a big improvement syntactically, and is perhaps more efficient:

B = A[I[np.newaxis, :], np.arange(Nj)[:, np.newaxis], np.arange(Nk)[np.newaxis, :]]

but is this the "right" way to do things?

-Nick