in src/vector_of_kll.cpp [248:255]
auto vector_of_kll_sketches<T, C>::is_empty() const -> Array1D<bool> {
auto vals = make_ndarray<bool>(d_);
auto view = vals.view();
for (uint32_t i = 0; i < d_; ++i) {
view(i) = sketches_[i].is_empty();
}
return vals;
}