Function TestMerge

cpp/src/arrow/util/tdigest_test.cc:150–193

TEST(TDigestTest, DISABLED_HugeVolume) { TestRandom(1U << 30); }

void TestMerge(const std::vector<std::vector<double>>& values_vector, uint32_t delta,
               double error_ratio) {
  const std::vector<double> quantiles = {0,   0.01, 0.1, 0.2, 0.3,  0.4, 0.5,
                                         0.6, 0.7,  0.8, 0.9, 0.99, 1};

  std::vector<TDigest> tds;
  for (const auto& values : values_vector) {
    TDigest td(delta);
    for (double value : values) {
      td.Add(value);
    }
    ASSERT_OK(td.Validate());
    tds.push_back(std::move(td));
  }

  std::vector<double> values_combined;
  for (const auto& values : values_vector) {
    values_combined.insert(values_combined.end(), values.begin(), values.end());
  }
  const std::vector<double> expected = ExactQuantile(values_combined, quantiles);

  // merge into an empty tdigest
  {
    TDigest td(delta);
    td.Merge(tds);
    ASSERT_OK(td.Validate());
    for (size_t i = 0; i < quantiles.size(); ++i) {
      const double tolerance = std::max(std::fabs(expected[i]) * error_ratio, 0.1);
      EXPECT_NEAR(td.Quantile(quantiles[i]), expected[i], tolerance) << quantiles[i];
    }
  }

  // merge into a non empty tdigest
  {
    TDigest td = std::move(tds[0]);
    tds.erase(tds.begin(), tds.begin() + 1);
    td.Merge(tds);
    ASSERT_OK(td.Validate());
    for (size_t i = 0; i < quantiles.size(); ++i) {
      const double tolerance = std::max(std::fabs(expected[i]) * error_ratio, 0.1);
      EXPECT_NEAR(td.Quantile(quantiles[i]), expected[i], tolerance) << quantiles[i];
    }
  }
}

// merge tdigests with same distribution
TEST(TDigestTest, MergeUniform) {