Most efficient way to add a value to a range of values in a list in Python?

Question

What is the most efficient way to add an integer to part of a list?

Example :

input : [1,5,3,7,4,3]

range of list to modify is 2,4

add 3 to range

output : [1,5,6,10,7,3]

Explanation :

First get the sublist using indexes 2 and 4. Then add 3 to the values in that index. then return a list containing the modified range.

I tried using a loop but its not fast enough. Need a faster method.

Can you share your attempt so we aren't giving you a worse solution? — user3483203, Jul 16 '18 at 03:15

score 6 · Answer 1 · answered Jul 16 '18 at 03:24

Adding a number to any number (supposedly sufficiently small as from the given eg.) is constant amount of time. You will have to iterate through those many list elements as in the provided range and add a number to them which is of the order of the length of the range. I don't think you can improve upon this task (i.e. which is asked in the question) although you can save some time on the overall program by handling the list as a generator object if you are dealing with very large amounts of data.

score 4 · Accepted Answer · answered Jul 16 '18 at 03:17

4

You can slice the list and then use iterator operations, which is faster than looping with an index:

l = [1,5,3,7,4,3]
l[2:5] = map((3).__add__, l[2:5])

l then becomes [1, 5, 6, 10, 7, 3].

answered Jul 16 '18 at 03:17

blhsing

91,368
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This is twice as slow as just `for i in range(2,4): l[i] += 3`, so no, this is not at all faster – user3483203 Jul 16 '18 at 03:18
1

thanks! I will try that out and mark it as answered if it works! – AutoBootDisk Jul 16 '18 at 03:18

Most efficient way to add a value to a range of values in a list in Python?

2 Answers2