Adding first value together from multiple lists

Question

I am trying to add the first values together in a series of lists then add the second values together from a series of lists and so on.

for example:

a=[10,20,30,40,50]
b=[60,70,80,90,100]
c=[110,120,130,140,150]

So as a result I want:

[180, 210,240, 270, 300]

The code I have so far is:

total = 0
for I in range (0,a)
total = total +a[I]+b[I]+c[I]
return total

Does this answer your question? [How to iterate through two lists in parallel?](https://stackoverflow.com/questions/1663807/how-to-iterate-through-two-lists-in-parallel) — buran, Dec 10 '21 at 15:39

score 1 · Answer 1 · answered Dec 10 '21 at 16:13

total = 0
for I in range (0,a):
    total = total +a[I]+b[I]+c[I]
return total

So, you have a few issues here with your code.

You can't use range(0,a). a is list and not an integer. You would have to use the length of list, or len(a).
You also aren't supposed to use capital letters as variables, unless they're constants variables, according to PEP8 standards.
You're trying to return data that isn't inside a function. That won't work. You could do something like:

def add_vals_from_lists(a,b,c):
    total = 0
    for i in range(len(a)):
        total += sum([a[i], b[i], c[i]])
        # The above is a much cleaner way to write total = total +a[I]+b[I]+c[I]
    return total

a=[10,20,30,40,50]
b=[60,70,80,90,100]
c=[110,120,130,140,150]

add_vals_from_lists(a,b,c)

Or, you could merely print(total) instead of using return total.

But, this will simply add everything to total returning 1200, not what you want.

As Samwise and Pedro noted, you can simply write this in a list-comprehension. [sum(t) for t in zip(a, b, c)]

zip() - Iterate over several iterables in parallel, producing tuples with an item from each one. For each of these tuples, (10,60,110) for the first one, the list-comprehension will sum() each one. Resulting in a list of [180, 210, 240, 270, 300].

Pedro Maia · Answer 2 · 2021-12-10T15:38:27.200

0

Use the sum and zip functions with a simple list comprehension:

total = [sum(i) for i in zip(a,b,c)]

Or iterate over the indexes:

total = []
for i in range(len(a)):
    total.append(a[i] + b[i] + c[i])

total has to be a list and you have to append to it on each iteration.

edited Dec 10 '21 at 15:38

answered Dec 10 '21 at 15:28

Pedro Maia

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score 0 · Answer 3 · answered Dec 10 '21 at 15:36

0

Use zip to get the first element of each list, and then sum them:

>>> a=[10,20,30,40,50]
>>> b=[60,70,80,90,100]
>>> c=[110,120,130,140,150]
>>> [sum(t) for t in zip(a, b, c)]
[180, 210, 240, 270, 300]

answered Dec 10 '21 at 15:36

Samwise

68,105
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score 0 · Answer 4 · answered Dec 10 '21 at 18:37

The indentation needs to be corrected in your code. Also, collect the sum of the elements of a particular index in a list. If you simply add the elements, it'll add all the elements give you only the sum of all the things. Also, in the for loop statement, it should be len(a) and not only a. Your corrected code:

a=[10,20,30,40,50]
b=[60,70,80,90,100]
c=[110,120,130,140,150]
sums=[]
for i in range(0,len(a)):
    sums.append(a[i]+b[i]+c[i])
print(sums)

Adding first value together from multiple lists

4 Answers4