CODEWITHSUNDEEP
pythonpython-3.x
Trace R.
Trace R.

Reputation: 347

How to execute a stepped increase of values in a list?

Let's say I have a list

A = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

I want to increase every 3rd number by a value of 5 to result in

A = [1, 2, 8, 4, 5, 11, 7, 8, 14, 10]

My gut tells me something along the lines of

A[::3] = [x + 5 for x in A]

OR using the loop below with replace somehow integrated

for num in range(0, len(A), 3):
    A = num + 5

Send help...thanks in advance.

Upvotes: 0

Views: 72

Answers (3)

Blorgbeard
Blorgbeard

Reputation: 103525

You almost had it with your first attempt.

Modify the slice to start at the 3rd element (index 2) per your example, and make sure to read the same slice that you're writing to:

A[2::3] = [x+5 for x in A[2::3]]

Upvotes: 1

krewsayder
krewsayder

Reputation: 446

You could make a function for it which would account for duplicate values or unsorted values. If my assumptions are not correct, you could easily adjust the function to get your values correct.

A = [1, 2, 3, 4, 5, 6, 10, 8, 9, 7]

def list_modifier(passed_list):

    passed_list.sort()

    mod_list = list(set(passed_list))

    out_list = {i:i if (mod_list.index(i)+1)%3 != 0 else (i+5) for i in mod_list }

    passed_list = [out_list[i] for i in out_list]

    return passed_list

list_modifier(A)

Returned list looks like this: [1, 2, 8, 4, 5, 11, 7, 8, 14, 10]

Upvotes: 0

SuperStew
SuperStew

Reputation: 3054

i think this will do it

A=[x+5 if i%3==0 else x for i,x in enumerate(A,1)]

Upvotes: 0

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