SparseMatrix NeighborhoodBuilder::buildMatrix_(std::vector<T>& entries, const DenseMatrix& mat) const
{
// Make sure, that there are no duplicate entries
std::sort(entries.begin(), entries.begin() + k_ * mat.rows(), triple_less);
auto new_end = std::unique(entries.begin(), entries.begin() + k_ * mat.rows(), triple_equal);
// An iterator for inserting the transposed entries
// This will also serve as the new end pointer of the
// entries array.
auto new_it = new_end;
// Symmetrize the matrix
for(auto old_it = entries.begin(); old_it != new_end; ++old_it, ++new_it) {
*new_it = T(old_it->col(), old_it->row(), old_it->value());
}
// Build the temporary matrix for the results
SparseMatrix result(mat.rowNames(), mat.rowNames());
// Fill the matrix and convert to CCS
// new_it points to the end of valid matrix entries.
result.matrix().setFromTriplets(entries.begin(), new_it);
result.matrix().makeCompressed();
return result;
}
