Add merge and reserve function to MetricValue (#315)

Summary:

Add merge and reserve function to MetricValue. Merge allow concatenation of other MetricValues.

Reviewed By: bigzachattack

Differential Revision: D64163319

dynolog/src/metric_frame/MetricValues.h

@@ -43,6 +43,10 @@ class MetricValues final {
     return *(begin() + idx);
   }
 
+  void reserve(const size_t size) {
+    data_.reserve(size);
+  }
+
   void resize(const size_t size) {
     data_.resize(size);
   }
@@ -77,6 +81,11 @@ class MetricValues final {
     return std::make_pair(*min_it, *max_it);
   }
 
+  void merge(const MetricValues<T>& other) {
+    data_.reserve(data_.size() + other.data_.size());
+    data_.insert(data_.end(), other.data_.begin(), other.data_.end());
+  }
+
  private:
   auto begin() const {
     return data_.begin();

dynolog/tests/metric_frame/MetricValuesTest.cpp

@@ -58,3 +58,22 @@ TEST(MetricValuesTest, aggTest) {
   EXPECT_TRUE(p50Maybe);
   EXPECT_EQ(p50Maybe.value(), 2.0);
 }
+
+TEST(MetricValuesTest, mergeTest) {
+  MetricValues<uint32_t> u, v;
+  for (int i = 0; i < 5; i++) {
+    u.push_back(i);
+  }
+  for (int i = 0; i < 5; i++) {
+    v.push_back(i);
+  }
+  EXPECT_EQ(u.size(), 5);
+
+  u.merge(v);
+  EXPECT_EQ(u.size(), 10);
+  EXPECT_EQ(u.sum(), 20);
+
+  auto avgMaybe = u.avg();
+  EXPECT_TRUE(avgMaybe);
+  EXPECT_EQ(avgMaybe.value(), 2.0);
+}