CODEWITHSUNDEEP
pythonpython-3.x
Divx
Divx

Reputation: 39

Incrementing elements in a list for a given variable range

Given that a list, has N elements. Suppose i represents the ith element of list_1 with all elements initially 0. Also there is a list:

a = [ 1 , 2 , 3, 4, ., . , N]

I need to increment elements in list_1 by 1, which are in the range [x-y , x+y] inclusive, where y is the ith element of list a.

I tried list comprehension, but could not come up with a possible way of doing it. I am new to python so I couldn't think about any other possible way!

Sample Input:

list_1 = [ 0, 0, 0, 0, 0] a = [ 1, 2, 3, 4, 5]

Sample Output:

list_1 = [5, 5, 4, 4, 3]

Example: The problem asks to increment elements that fall in the given range i.e. say x-y= 0 and x+y = 4 , it means increment 0th, 1st, 2nd , 3rd and 4th element of the list.

I would like to know a way to get the desired list, and overcoming the errors.

Upvotes: 0

Views: 1299

Answers (1)

StardustGogeta
StardustGogeta

Reputation: 3406

I think this is what you are looking for. This will increment in the range of indices x-y to x+y.

list_1 = list(range(10))

def incList(ls, x, y):
    return [e + 1 if x-y <= i <= x+y else e for i, e in enumerate(ls)]

print(incList(list_1, x=3, y=2))
print(incList(list_1, x=3, y=4))

Output:

[0, 2, 3, 4, 5, 6, 6, 7, 8, 9]
[1, 2, 3, 4, 5, 6, 7, 8, 8, 9]

You can use enumerate to check the index and manipulate the element value in a single list comprehension.

Alternatively, if you want to iterate from the x-yth element to the x+yth element, use x-y-1 <= i <= x+y-1 in the list comprehension instead.

EDIT:

The original question suggested that a copy of the list with incremented values is fine, but the comments suggest otherwise. In order to change the original list directly, we can make a small alteration to the function.

def incList(ls, x, y):
    for i in range(max(0, x-y), min(len(ls), x+y+1)):
        ls[i] += 1

As before, change x-y and x+y+1 to x-y-1 and x+y if desired.

Upvotes: 3

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