KK Sasa <genwei...@gmail.com> writes: > 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.
Why didn't you follow Mark Lawrence's advice? In your problem, results is a list of N sublists, each containing exactly four numerical values, Let's try with N=2 In [36]: results = [d2(t[k]) for k in range(2)] In [37]: print results [[1, 2, 3, 4], [5, 6, 7, 8]] Let's try the obvious method to sum In [38]: [sum(el) for el in results] Out[38]: [10, 26] not what you're looking for, but what if we had In [39]: [sum(el) for el in zip(*results)] Out[39]: [6, 8, 10, 12] correct. BTW, as you're using the scientific stack the answer of Christian Gollwitzer is the more appropriate. -- https://mail.python.org/mailman/listinfo/python-list
