void kmeans_1d_dp(const double *x, const size_t N, const double *y,
size_t Kmin, size_t Kmax,
int* cluster, double* centers,
double* withinss, int* size)
{
// Input:
// x -- an array of double precision numbers, not necessarily sorted
// Kmin -- the minimum number of clusters expected
// Kmax -- the maximum number of clusters expected
// NOTE: All vectors in this program is considered starting at position 0.
std::vector<double> x_sorted(N);
std::vector<double> y_sorted;
auto is_equally_weighted(true);
std::vector<size_t> order(N);
//Number generation using lambda function, not supported by all g++:
//std::size_t n(0);
//std::generate(order.begin(), order.end(), [&]{ return n++; });
for(size_t i=0; i<order.size(); ++i) {
order[i] = i;
}
// Sort the index of x in increasing order of x
// Sorting using lambda function, not supported by all g++ versions:
// std::sort(order.begin(), order.end(),
// [&](size_t i1, size_t i2) { return x[i1] < x[i2]; } );
struct CompareIndex {
const double * m_x;
CompareIndex(const double * x) : m_x(x) {}
bool operator() (size_t i, size_t j) { return (m_x[i] < m_x[j]);}
} compi(x);
std::sort(order.begin(), order.end(), compi);
for(size_t i=0; i<order.size(); ++i) {
x_sorted[i] = x[order[i]];
}
// check to see if unequal weight is provided
if(y != NULL) {
is_equally_weighted = true;
for(size_t i=1; i<N; ++i) {
if(y[i] != y[i-1]) {
is_equally_weighted = false;
break;
}
}
}
if(! is_equally_weighted) {
y_sorted.resize(N);
for(size_t i=0; i<order.size(); ++i) {
y_sorted[i] = y[order[i]];
}
}
const size_t nUnique = numberOfUnique(x_sorted.begin(), x_sorted.end());
Kmax = nUnique < Kmax ? nUnique : Kmax;
if(nUnique > 1) { // The case when not all elements are equal.
std::vector< std::vector< double > > S( Kmax, std::vector<double>(N) );
std::vector< std::vector< size_t > > J( Kmax, std::vector<size_t>(N) );
size_t Kopt;
// Fill in dynamic programming matrix
if(is_equally_weighted) {
fill_dp_matrix(x_sorted, S, J);
// Choose an optimal number of levels between Kmin and Kmax
Kopt = select_levels(x_sorted, J, Kmin, Kmax);
} else {
fill_weighted_dp_matrix(x_sorted, y_sorted, S, J);
// Choose an optimal number of levels between Kmin and Kmax
Kopt = select_levels_weighted(x_sorted, y_sorted, J, Kmin, Kmax);
}
if (Kopt < Kmax) { // Reform the dynamic programming matrix S and J
J.erase(J.begin() + Kopt, J.end());
}
std::vector<int> cluster_sorted(N);
// Backtrack to find the clusters beginning and ending indices
if(is_equally_weighted) {
backtrack(x_sorted, J, &cluster_sorted[0], centers, withinss, size);
} else {
backtrack_weighted(x_sorted, y_sorted, J, &cluster_sorted[0], centers, withinss, size);
}
for(size_t i = 0; i < N; ++i) {
// Obtain clustering on data in the original order
cluster[order[i]] = cluster_sorted[i];
}
} else { // A single cluster that contains all elements
for(size_t i=0; i<N; ++i) {
cluster[i] = 0;
}
centers[0] = x[0];
withinss[0] = 0.0;
size[0] = N * (is_equally_weighted ? 1 : y[0]);
}
} //end of kmeans_1d_dp()
ClusterResult
kmeans_1d_dp(const std::vector<double> & x, size_t Kmin, size_t Kmax)
{
// Input:
// x -- a vector of numbers, not necessarily sorted
// Kmin -- the minimum number of clusters expected
// Kmax -- the maximum number of clusters expected
// NOTE: All vectors in this program is considered starting at position 1,
// position 0 is not used.
ClusterResult result;
const size_t N = x.size() - 1; // N: is the size of input vector
std::vector<double> x_sorted(x);
std::sort(x_sorted.begin()+1, x_sorted.end());
const size_t nUnique = numberOfUnique(x_sorted.begin()+1, x_sorted.end());
Kmax = nUnique < Kmax ? nUnique : Kmax;
if(nUnique > 1) { // The case when not all elements are equal.
std::vector< std::vector< double > > D( (Kmax + 1), std::vector<double>(N + 1) );
std::vector< std::vector< size_t > > B( (Kmax + 1), std::vector<size_t>(N + 1) );
// Fill in dynamic programming matrix
fill_dp_matrix(x_sorted, D, B);
// Choose an optimal number of levels between Kmin and Kmax
size_t Kopt = select_levels(x_sorted, B, Kmin, Kmax);
if (Kopt < Kmax) { // Reform the dynamic programming matrix D and B
B.erase(B.begin()+ Kopt + 1, B.end());
}
// Backtrack to find the clusters beginning and ending indices
backtrack(x_sorted, B, result);
// Perform clustering on the original data
for(size_t i = 1; i < x.size(); ++i) {
size_t indexLeft = 1;
size_t indexRight;
for (size_t k = 1; k < result.size.size(); ++k) {
indexRight = indexLeft + result.size[k] - 1;
if ( x[i] <= x_sorted[indexRight] ) {
result.cluster[i] = k;
break;
}
indexLeft = indexRight + 1;
}
}
} else { // A single cluster that contains all elements
result.nClusters = 1;
result.cluster = std::vector<size_t>(N + 1, 1);
result.centers.resize(2);
result.withinss.resize(2);
result.size.resize(2);
result.centers[1] = x[1];
result.withinss[1] = 0.0;
result.size[1] = N;
}
return result;
} //end of kmeans_1d_dp()
