Write a function that adds lists elements using *args

Question

I would like to write a function that calculates scalar sum of several vectors. It should take several lists as arguments eg.

def add_lists(x, y, z):
   # return sum of x, y, z

x = add_lists([1, 2],[2, 1],[3, 1])
# x returns [6, 4]

It is easy to do it for only two arguments, but how can I do it using *args if they are more than two, so that my add_lists will return [6, 4]?

check this https://stackoverflow.com/questions/919680/can-a-variable-number-of-arguments-be-passed-to-a-function — NishanthSpShetty, Dec 07 '17 at 11:28
How would you sum it if passed a `list` of two-`tuple`s? The answer is the same. — ShadowRanger, Dec 07 '17 at 11:28
@NishanthShetty: That other question asks is varargs is possible, but the OP clearly knows about `*args`... — ShadowRanger, Dec 07 '17 at 11:29

score 4 · Answer 1 · answered Dec 07 '17 at 11:29

4

You can use zip and *args:

def add_lists(*args):
    return [sum(x) for x in zip(*args)]

x = add_lists([1, 2],[2, 1],[3, 1])
# x is [6, 4]

answered Dec 07 '17 at 11:29

Matias Cicero

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This is the best and most general solution, and unlike other solutions here will automatically scale up if the length of all "vectors" changes. – DeepSpace Dec 07 '17 at 11:31
1

What I like here is that `zip(*args)` and `def add_lists(*args)` is using the `*` operator in two different ways: The first way is to demonstrate that multiple arguments can be passed through, whereas the second way is actually unpacking `args` into the `zip` function – TerryA Dec 07 '17 at 11:33

score 1 · Answer 2 · answered Dec 07 '17 at 11:30

1

You can also do it this way:

def add_lists(*args):
    s1 = sum(i[0] for i in args)
    s2 = sum(i[1] for i in args)
    return [s1,s2]

res = add_lists([1, 2],[2, 1],[3, 1])
print(res)

Output:

[6, 4]

answered Dec 07 '17 at 11:30

Vasilis G.

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score 0 · Accepted Answer · answered Dec 07 '17 at 11:28

If I am understanding your question correctly, you wish to write a function that can take any amount of vectors and return the sum? Then yes, you would need to use *args like so:

def add_lists(*args):
    final_vector = [0, 0]
    for vector in args:
        final_vector[0] += vector[0]
        final_vector[1] += vector[1]
    return final_vector

Basically, treat args as a list - containing all the arguments passed through when you call the function.

This is exactly what I need! Thank you! – krakowi Dec 07 '17 at 11:31 — krakowi, Dec 07 '17 at 11:31

Write a function that adds lists elements using *args

3 Answers3