Second Differences

Problem

Return the second differences of a series, defined by x[t] - 2 * x[t-1] + x[t-2] for t from 2 onward. This is the result of applying the differencing operator twice and removes a linear trend from the data.

Return an empty list when the series has fewer than three values.

Hint

Second differences are the differences of the first differences.

Test cases

case 1

in: [[1,4,9,16]]

expected: [2,2]

case 2

in: [[1,2,3]]

expected: [0]

case 3

in: [[1,1]]

expected: []

case 4

in: [[5]]

expected: []

Starter codePython

def second_differences(series):
    # Your code here
    pass

4 test cases · run your code against them in the editor