Cohort Retention Mean

Problem

Compute the mean retention for a period across cohorts. retention_matrix[c][p] is the fraction of cohort c retained in period p; rows shorter than period + 1 are skipped.

Return 0.0 when no cohort has that period.

Hint

Younger cohorts have not lived long enough to contribute to later periods.

Test cases

case 1

in: [[[1,0.5,0.2],[1,0.4],[1,0.6,0.3]],1]

expected: 0.5

case 2

in: [[[1,0.5,0.2],[1,0.4],[1,0.6,0.3]],2]

expected: 0.25

case 3

in: [[[1,0.5],[1,0.5]],0]

expected: 1

case 4

in: [[[1]],3]

expected: 0

Starter codePython

def cohort_retention_mean(retention_matrix, period):
    # Your code here
    pass

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