Combining NumPy arrays

Question

I have two 20x100x3 NumPy arrays which I want to combine into a 40 x 100 x 3 array, that is, just add more lines to the array. I am confused by which function I want: is it

Answer 1

One of the best ways of learning is experimenting, but I would say you want np.vstack although there are other ways of doing the same thing:

a = np.ones((20,100,3))
b = np.vstack((a,a)) 

print b.shape # (40,100,3)

or

b = np.concatenate((a,a),axis=0)

EDIT

Just as a note, on my machine for the sized arrays in the OP's question, I find that np.concatenate is about 2x faster than np.vstack

In [172]: a = np.random.normal(size=(20,100,3))

In [173]: c = np.random.normal(size=(20,100,3))

In [174]: %timeit b = np.concatenate((a,c),axis=0)
100000 loops, best of 3: 13.3 us per loop

In [175]: %timeit b = np.vstack((a,c))
10000 loops, best of 3: 26.1 us per loop