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i'm using Python and I have the following list A = [10,20,30,40] how can obtain a new list such as I'm adding the second element to the first, the third to the second and fourth to the third. Meaning the output would be [30,50,70].

Nael Jn Baptiste -aka Analyze
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3 Answers3

3

Can use simple list comprehension like this:

a = [10,20,30,40]
b = [a[i] + a[i+1] for i in range(len(a)-1)]

b
[30, 50, 70]
Shubham Periwal
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2

Take a look at the pairwise recipe from the itertools module (which will be added as a function of itertools in 3.10). Once you've copied that, you can just do:

[x + y for x, y in pairwise(A)]

or for fun with less custom code, add imports from operator import add and from itertools import starmap and you can make an iterator that produces the results lazily with:

starmap(add, pairwise(A))  # Wrap in list if you need a list
ShadowRanger
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a = [10,20,30,40,50]
new_list = []
for i in range(1, len(a)):
    new_list.append(a[i] + a[i-1])

When we do range(1, len(a)), we create a set of indexes which are [1,2,3,4].

So when we do: for i in range(1, len(a)): it's kind of like doing for i in range [1,2,3,4].

If we now imagine we are doing:

for i in [1,2,3,4]:
    new_list.append(a[i] + a[i-1])

What it's doing is getting the current value of a at i and adding it a at the previous index i-1 and appending the result to a new list.

Salaah Amin
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