问题:

Is there an easy way to compute the element-wise sum of N lists in python? I know if we have n lists defined (call the ith list c_i), we can do:

z = [sum(x) for x in zip(c_1, c_2, ...)]

For example:

c1 = [1,2]
c2 = [3,4]
c3 = [5,6]
z  = [sum(x) for x in zip(c1,c2,c3)]

Here z = [9, 12]

But what if we don't have c_i defined and instead have c_1...c_n in a list C?

Is there a similar way to find z if we just have C?

I hope this is clear.

resolved: I was wondering what the * operator was all about...thanks!

回答1:

Just do this:

[sum(x) for x in zip(*C)]

In the above, C is the list of c_1...c_n. As explained in the link in the comments (thanks, @kevinsa5!):

* is the "splat" operator: It takes a list as input, and expands it into actual positional arguments in the function call.

For additional details, take a look at the documentation, under "unpacking argument lists" and also read about calls (thanks, @abarnert!)

This isn't all that different from Óscar López's answer, but uses itertools.imap instead of a list comprehension.

from itertools import imap
list(imap(sum, zip(*C))