Merge pull request #433 from dvadym/quantile_tree_merge

Implement QuantileTree.Merge method

src/bindings/PyDP/algorithms/qunatile_tree.cpp

@@ -30,21 +30,21 @@ std::unique_ptr<dp::QuantileTree<double>> CreateQuantileTree(double lower, doubl
 
 dp::QuantileTree<double>::Privatized GetPrivatizeTree(
     dp::QuantileTree<double>& tree, double epsilon, double delta,
-    int max_partitions_contributed_to, int max_contributions_per_partition,
+    int max_partitions_contributed, int max_contributions_per_partition,
     const std::string& noise_type) {
   dp::QuantileTree<double>::DPParams dp_params;
   dp_params.epsilon = epsilon;
   dp_params.delta = delta;
   dp_params.max_contributions_per_partition = max_contributions_per_partition;
-  dp_params.max_partitions_contributed_to = max_partitions_contributed_to;
+  dp_params.max_partitions_contributed_to = max_partitions_contributed;
   // Create DP mechanism.
   if (noise_type == "laplace") {
     dp_params.mechanism_builder = std::make_unique<dp::LaplaceMechanism::Builder>();
   } else if (noise_type == "gaussian") {
     dp_params.mechanism_builder = std::make_unique<dp::GaussianMechanism::Builder>();
   } else {
     throw py::value_error("noise_type can be 'laplace' or 'gaussian', but it is '" +
-                          noise_type + "'./**/");
+                          noise_type + "'.");
   }
   auto status_or_result = tree.MakePrivate(dp_params);
   if (!status_or_result.ok()) {
@@ -89,15 +89,28 @@ void init_algorithms_quantile_tree(py::module& m) {
     to_return.mutable_data()->PackFrom(obj.Serialize());
     return to_return;
   });
-  py_class.def("merge", &dp::QuantileTree<double>::Merge, py::arg("summary"));
+  py_class.def(
+      "merge",
+      [](dp::QuantileTree<double>& tree, const dp::Summary& summary) {
+        if (!summary.has_data()) {
+          throw std::runtime_error("Cannot merge summary, no data.");
+        }
+
+        dp::BoundedQuantilesSummary quantiles_summary;
+        if (!summary.data().UnpackTo(&quantiles_summary)) {
+          throw std::runtime_error("Fail to upack data");
+        }
+        tree.Merge(quantiles_summary);
+      },
+      py::arg("summary"));
 
   py_class.def(
       "compute_quantiles",
       [](dp::QuantileTree<double>& tree, double epsilon, double delta,
-         int max_partitions_contributed_to, int max_contributions_per_partition,
+         int max_partitions_contributed, int max_contributions_per_partition,
          const std::vector<double>& quantiles, const std::string& noise_type) {
         dp::QuantileTree<double>::Privatized privatized_tree =
-            GetPrivatizeTree(tree, epsilon, delta, max_partitions_contributed_to,
+            GetPrivatizeTree(tree, epsilon, delta, max_partitions_contributed,
                              max_contributions_per_partition, noise_type);
 
         std::vector<double> output;
@@ -110,18 +123,18 @@ void init_algorithms_quantile_tree(py::module& m) {
         }
         return output;
       },
-      py::arg("epsilon"), py::arg("delta"), py::arg("max_partitions_contributed_to"),
+      py::arg("epsilon"), py::arg("delta"), py::arg("max_partitions_contributed"),
       py::arg("max_contributions_per_partition"), py::arg("quantiles"),
       py::arg("noise_type") = "laplace", "Compute multiple quantiles.");
 
   py_class.def(
       "compute_quantiles_and_confidence_intervals",
       [](dp::QuantileTree<double>& tree, double epsilon, double delta,
-         int max_contributions_per_partition, int max_partitions_contributed_to,
+         int max_contributions_per_partition, int max_partitions_contributed,
          const std::vector<double>& quantiles, double confidence_interval_level,
          const std::string& noise_type) {
         dp::QuantileTree<double>::Privatized privatized_tree =
-            GetPrivatizeTree(tree, epsilon, delta, max_partitions_contributed_to,
+            GetPrivatizeTree(tree, epsilon, delta, max_partitions_contributed,
                              max_contributions_per_partition, noise_type);
 
         std::vector<QuantileConfidenceInterval> output;
@@ -142,7 +155,7 @@ void init_algorithms_quantile_tree(py::module& m) {
         }
         return output;
       },
-      py::arg("epsilon"), py::arg("delta"), py::arg("max_partitions_contributed_to"),
+      py::arg("epsilon"), py::arg("delta"), py::arg("max_partitions_contributed"),
       py::arg("max_contributions_per_partition"), py::arg("quantiles"),
       py::arg("confidence_interval_level"), py::arg("noise_type") = "laplace",
       "Compute multiple quantiles and confidence intervals for them.");

tests/algorithms/test_quantile_tree.py

@@ -1,5 +1,6 @@
 import pytest
 
+import pydp._pydp as dp
 from pydp.algorithms.quantile_tree import QuantileTree
 
 
@@ -70,3 +71,33 @@ def test_quantiles_and_confidence_intervals(self):
                 <= dp_quantile_ci.upper_bound
             )
             assert dp_quantile_ci.upper_bound - dp_quantile_ci.lower_bound < 0.01
+
+    def test_serialize_deserialize(self):
+        lower, upper = 0, 1000
+        height, branching_factor = 5, 10
+        tree1 = QuantileTree(lower, upper, height, branching_factor)
+
+        # Add elements 0,..1000 to the tree.
+        for i in range(1001):
+            tree1.add_entry(i)
+
+        serialized_tree = tree1.serialize().to_bytes()
+
+        # Deserialize
+        # 1.Create empty tree with the same parameters.
+        tree2 = QuantileTree(lower, upper, height, branching_factor)
+        # 2. Merge serialized_tree to tree2.
+        tree2.merge(dp.bytes_to_summary(serialized_tree))
+
+        # Check that tree2 computes correct quantiles. For this use high
+        # epsilon, which means small noise and close to the real quantiles.
+        eps, delta = 10000, 0
+        quantiles_to_compute = [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9, 0.9]
+        dp_quantiles = tree2.compute_quantiles(
+            eps, delta, 1, 1, quantiles_to_compute, "laplace"
+        )
+
+        # Check that DP quantiles are close to expected.
+        for quantile, dp_quantile in zip(quantiles_to_compute, dp_quantiles):
+            expected_quantile = quantile * upper
+            assert abs(expected_quantile - dp_quantile) < 0.1