Lag-k Series

Problem

Return the lag-k series, i.e. the values x[t-k] for t = k, ..., n-1. The result is the original series shifted down by k positions and is therefore k elements shorter.

Return an empty list if k is negative or k is not smaller than the series length; k = 0 returns a copy of the series.

Hint

The first k output values are the first n - k inputs.

Test cases

case 1

in: [[1,2,3,4],1]

expected: [1,2,3]

case 2

in: [[1,2,3,4],2]

expected: [1,2]

case 3

in: [[1,2,3],3]

expected: []

case 4

in: [[9,8,7,6,5],0]

expected: [9,8,7,6,5]

Starter codePython

def lag_series(series, k):
    # Your code here
    pass

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