On 12 December 2014 at 06:22, KK Sasa <genwei...@gmail.com> wrote: > Hi there, > > The list comprehension is results = [d2(t[k]) for k in xrange(1000)], where > d2 is a function returning a list, say [x1,x2,x3,x4] for one example. So > "results" is a list consisting of 1000 lists, each of length four. Here, what > I want to get is the sum of 1000 lists, and then the result is a list of > length four. Is there any efficient way to do this? Because I found it is > slow in my case. I tried sum(d2(t[k]) for k in xrange(1000)), but it returned > error: TypeError: unsupported operand type(s) for +: 'int' and 'list'. Thanks.
Use numpy.sum: >>> import numpy as np >>> a = [[1, 1, 1, 1], [2, 2, 2, 2], [3, 3, 3, 3]] >>> np.sum(a, 0) array([6, 6, 6, 6]) >>> np.sum(a, 1) array([ 4, 8, 12]) The second argument to numpy.sum is the dimension along which you want to sum e.g. rows or columns. Oscar -- https://mail.python.org/mailman/listinfo/python-list
