Function ArgSort

src/common/algorithm.h:80–87

template <typename Idx, typename Iter, typename V = typename std::iterator_traits<Iter>::value_type,
          typename Comp = std::less<V>>
std::vector<Idx> ArgSort(Context const *ctx, Iter begin, Iter end, Comp comp = std::less<V>{}) {
  auto n = std::distance(begin, end);
  std::vector<Idx> result(n);
  Iota(ctx, result.begin(), result.end(), 0);
  auto op = [&](Idx const &l, Idx const &r) { return comp(begin[l], begin[r]); };
  StableSort(ctx, result.begin(), result.end(), op);
  return result;
}
}  // namespace common
}  // namespace xgboost