cdef double ARI = 0.0

if pred.shape[0] != expect.shape[0]:

raise Exception("pred and expect must have the same length.")

cdef int N = pred.shape[0]

cdef int M = N * (N - 1) / 2

cdef int a = 0 # number of pairs that belong to the same class and the same cluster

cdef b = 0 # number of pairs that belong to the same class but different clusters

cdef c = 0 # number of pairs that belong to different classes but the same cluster

cdef int i = 0

cdef int j = 0

for i in range(N - 1):

for j in range(i + 1, N):

if expect[i] == expect[j] and pred[i] == pred[j]:

a += 1

elif expect[i] == expect[j] and pred[i] != pred[j]:

b += 1

elif expect[i] != expect[j] and pred[i] == pred[j]:

c += 1

ARI = (a - ((a+c)*(a+b) / M)) / ( (((a+c)+(a+b)) / 2.0) - ((a+c)*(a+b) / M) )

return ARI