numpy: Efficiently avoid 0s when taking log(matrix)

Question

from numpy import *

m = array([[1,0],
           [2,3]])

I would like to compute the element-wise log2(m), but only in the places whe

Answer 1

Another option is to use the where parameter of numpy's ufuncs:

m = np.array([[1., 0], [2, 3]])
res = np.log2(m, out=np.zeros_like(m), where=(m!=0))

No RuntimeWarning is raised, and zeros are introduced where the log is not computed.