Seasonal Indices Simple Average

Problem

Estimate multiplicative seasonal indices by simple averaging. Compute the overall mean, then for each season position j = 0, ..., period-1 average the values whose indices are congruent to j modulo period, and divide that average by the overall mean.

Return the list of period indices. Return an empty list if period is not positive or exceeds the series length; if the overall mean is exactly 0.0 return a list of period zeros.

Hint

Python slicing with a step of period gives one season position at a time.

Test cases

case 1

in: [[2,4,6,2,4,6],3]

expected: [0.5,1,1.5]

case 2

in: [[1,3,5,2,4,6],3]

expected: [0.42857142857142855,1,1.5714285714285714]

case 3

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

expected: [0.8,1.2]

case 4

in: [[1,2,3],5]

expected: []

Starter codePython

def seasonal_indices(series, period):
    # Your code here
    pass

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