Finding the difference between consecutive numbers in a list (Python)
deviation, python, recursion
Solution
You can do:
[y-x for x, y in zip(A[:-1], A[1:])]
>>> A = [1, 10, 100, 50, 40]
>>> [y-x for x, y in zip(A[:-1], A[1:])]
[9, 90, -50, -10]
Note that the difference will be negative if the right side is smaller, you can easily fix this (If you consider this wrong), I'll leave the solution for you.
Explanation:
The best explanation you can get is simply printing each part of the list comprehension.
- `A[:-1]` returns the list without the last element: `[1, 10, 100, 50]`
- `A[1:]` returns the list without the first element: `[10, 100, 50, 40]`
- `zip(A[:-1], A[1:])` returns `[(1, 10), (10, 100), (100, 50), (50, 40)]`
- The last step is simply returning the difference in each tuple.
Problem
Given a list of numbers, I am trying to write a code that finds the difference between consecutive elements. For instance, `A = [1, 10, 100, 50, 40]` so the output of the function should be `[0, 9, 90, 50, 10]`. Here is what I have so far trying to use recursion: ``` def deviation(A): if len(A) < 2: return else: return [abs(A[0]-A[1])] + [deviation(A[1: ])] ``` The output I get, however, (using the above example of A as the input) is `[9, [90, [50, [10, None]]]]`. How do I properly format my brackets? (I've tried guessing and checking but I this is the closest I have gotten) And how do I write this where it subtracts the current element from the previous element without getting an index error for the first element? I still want the first element of the output list to be zero but I do not know how to go about this using recursion and for some reason that seems the best route to me.