Ignoring -Inf values in arrays using numpy/scipy in Python

Question

I have an NxM array in numpy that I would like to take the log of, and ignore entries that were negative prior to taking the log. When I take the log of negative entries, it

Answer 1

Use masked arrays:

>>> a = numpy.array([2, 0, 1.5, -3])
>>> b = numpy.ma.log(a)
>>> b
masked_array(data = [0.69314718056 -- 0.405465108108 --],
             mask = [False  True False  True],
       fill_value = 1e+20)

>>> b.sum()
1.0986122886681096