virtual double compute( const Clustering& c1, const Clustering& c2 ) const {
size_t c1_sum2 = 0;
size_t n = 0;
for (size_t i=0; i < c1.size(); i++) {
c1_sum2 += c1[i].size() * c1[i].size();
n += c1[i].size();
}
size_t c2_sum2 = 0;
for (size_t i=0; i < c2.size(); i++) {
c2_sum2 += c2[i].size() * c2[i].size();
}
size_t c1c2_sum2 = 0;
for (size_t i=0; i < c1.size(); i++) {
for (size_t j=0; j < c2.size(); j++) {
size_t size;
std::set_intersection( c1[i].begin(), c1[i].end(),
c2[j].begin(), c2[j].end(),
counter(size) );
c1c2_sum2 += size * size;
}
}
return ( c1_sum2 + c2_sum2 - (2 * c1c2_sum2) ) / (double)(n*n);
}
