Adjusted Rand Index

Problem

Compute the adjusted Rand index between two label lists using pair counts:

ARI = (sum_ij C(n_ij, 2) - E) / (0.5 * (sum_i C(a_i, 2) + sum_j C(b_j, 2)) - E), where E = sum_i C(a_i, 2) * sum_j C(b_j, 2) / C(n, 2).

Return 1.0 when the denominator is 0, and 0.0 for empty input.

Hint

ARI corrects the Rand index for chance using counting pairs that fall in the same cluster.

case 1

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

expected: 1

case 2

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

expected: -0.49999999999999994

case 3

in: [[0,0,1,1,2,2],[0,0,1,2,1,2]]

expected: 0.16666666666666669

case 4

in: [[],[]]

expected: 0

Starter codePython

def adjusted_rand_index(a, b):
    # Your code here
    pass

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