Method GetLastIndices

cpp/src/arrow/dataset/scanner_test.cc:1780–1788

Given a vector of fragment indices (one per batch) return a vector (one per fragment) mapping fragment index to the last occurrence of that index in order This allows us to know when to mark a fragment as finished

  //
  // This allows us to know when to mark a fragment as finished
  std::vector<int> GetLastIndices(const std::vector<int>& order) {
    std::vector<int> last_indices(kNumFragments);
    for (std::size_t i = 0; i < kNumFragments; i++) {
      auto last_p = std::find(order.rbegin(), order.rend(), static_cast<int>(i));
      EXPECT_NE(last_p, order.rend());
      last_indices[i] = static_cast<int>(std::distance(last_p, order.rend())) - 1;
    }
    return last_indices;
  }

  /// We buffer one item in order to enumerate it (technically this could be avoided if
  /// delivering in order but easier to have a single code path).  We also can't deliver