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Re: list comprehension return a list and sum over in loop

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On 12 December 2014 at 06:22, KK Sasa <genwei007@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

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list comprehension return a list and sum over in loop KK Sasa <genwei007@gmail.com> - 2014-12-11 22:22 -0800
  Re: list comprehension return a list and sum over in loop Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-12-12 07:17 +0000
    Re: list comprehension return a list and sum over in loop KK Sasa <genwei007@gmail.com> - 2014-12-12 00:30 -0800
      Re: list comprehension return a list and sum over in loop Christian Gollwitzer <auriocus@gmx.de> - 2014-12-12 10:09 +0100
      Re: list comprehension return a list and sum over in loop Peter Otten <__peter__@web.de> - 2014-12-12 10:13 +0100
        Re: list comprehension return a list and sum over in loop KK Sasa <genwei007@gmail.com> - 2014-12-12 01:45 -0800
          Re: list comprehension return a list and sum over in loop Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2014-12-12 13:12 +0200
            Re: list comprehension return a list and sum over in loop Peter Otten <__peter__@web.de> - 2014-12-12 13:32 +0100
              Re: list comprehension return a list and sum over in loop KK Sasa <genwei007@gmail.com> - 2014-12-12 05:09 -0800
                Re: list comprehension return a list and sum over in loop Peter Otten <__peter__@web.de> - 2014-12-12 17:08 +0100
                Re: list comprehension return a list and sum over in loop KK Sasa <genwei007@gmail.com> - 2014-12-12 19:04 -0800
                Re: list comprehension return a list and sum over in loop Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-12-13 11:27 +0000
            Re: list comprehension return a list and sum over in loop KK Sasa <genwei007@gmail.com> - 2014-12-12 05:03 -0800
  Re: list comprehension return a list and sum over in loop Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-12-12 20:46 +1100
  Re: list comprehension return a list and sum over in loop Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-12-12 16:47 +0000
  Re: list comprehension return a list and sum over in loop pecore@pascolo.net - 2014-12-13 13:38 +0100

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