Get mean of 2D slice of a 3D array in numpy

Question

I have a numpy array with a shape of:

(11L, 5L, 5L)

I want to calculate the mean over the 25 elements of each \'slice\' of the array [0, :,

Answer 1

You can reshape(11, 25) and then call mean only once (faster):

a.reshape(11, 25).mean(axis=1)

Alternatively, you can call np.mean twice (about 2X slower on my computer):

a.mean(axis=2).mean(axis=1)