CODEWITHSUNDEEP
python
Helen Neely
Helen Neely

Reputation: 4740

Finding the sum of a list

Just looking for a more efficient approach to adding a very large number in a list together. I know I can use the sum() function, but I'm wondering if there is any other better or efficient approach.

nums = list(range(17832931))
ans = sum(nums)

Thanks for your suggestions

Upvotes: 0

Views: 129

Answers (5)

Nusab19
Nusab19

Reputation: 125

Okay, so everyone has answered. To sum from 1 to n, @Nick's answer is the best advise.

But if you just have a iterable and want to sum of it. Just use the sum function.

Remember not to convert it to list or tuple. Just use sum in the iterable.

Here's what I mean:

nums = range(17832931)
ans = sum(nums)

When you convert the nums to a list, it takes O(n) time to do that; which is completely unnecessary. Example:

nums = range(17832931)
ans = sum(nums) # takes O(n) time
     # Total: O(n) 

nums = list(range(17832931)) # takes O(n) time
ans = sum(nums) # takes O(n) time
     # Total: O( 2n )

Conclusion

In python, there's no other function or method to optimize the sum of values.

However, if you can figure out what kind of values you have, then you do it in O(1) complexity by using some math formula. As @Nick used n(n+1)/2

Upvotes: 0

hello_friend
hello_friend

Reputation: 5788

nums = list(range(17832931))
ans = [*map(lambda N:  (N*(N+1))/2, [nums[len(nums)-1]])]
print(ans)

Upvotes: 0

Shivam Bharadwaj
Shivam Bharadwaj

Reputation: 2296

One of the solution could be using Lambda function. Refer this article

final_sum = sum(map(lambda x: x, list(range(26363637))))
print(final_sum)

# Output : 347520664752066

In the bove solution, I've used a lambda function and mapped each value using map function and then uses inbuilt function sum which will add each iterable and will return the sum

Upvotes: 1

Rafael
Rafael

Reputation: 1

You can use this approach : 

sum = 0 
number_list = list(range(26363637))
for number in number_list:
    sum += number 
print(sum)

Upvotes: 0

Nick
Nick

Reputation: 147166

If you're just trying to sum the numbers in a range, you can simply use (n-1)*n//2. For example:

n = 100
print(sum(range(n)))
print((n-1)*n//2)

Output

4950
4950

Upvotes: 5

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