Sum nested lists in Python

Question

I have a nested list in python, i=[[1,2,3],[4,5,6]]. I want to sum the terms such that the final result is j=[1+4,2+5,6+3]. I have tried:

i=[[1,2,3],[4,5,6]]
j=[sum(x) for x in zip(i)]

But this is what I get instead:

>>>print j
[6, 15]

Of course both answers are correct. I have to give credit to the first one though. Thanks! — hat
– hat, Commented Mar 11, 2014 at 7:51

Valentin Lorentz · Accepted Answer · 2014-03-11 07:43:20Z

2

zip does not take a list of lists as an argument. It takes an arbitrary long list of list arguments.

Here is how to do it:

i=[[1,2,3],[4,5,6]]
j=[sum(x) for x in zip(*i)]

answered Mar 11, 2014 at 7:37

Valentin Lorentz

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Comments

embert · Accepted Answer · 2014-03-11 07:38:04Z

1

You forgot the *

>>> i=[[1,2,3],[4,5,6]]
>>> [sum(x) for x in zip(*i)]
[5, 7, 9]

answered Mar 11, 2014 at 7:38

embert

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