From 369dc4c8b3331aa318f2a98eb973d0840541297d Mon Sep 17 00:00:00 2001
From: Douglas Rumbaugh <dbr4@psu.edu>
Date: Mon, 3 Jul 2023 16:52:11 -0400
Subject: Slightly optimized merge function

---
 include/shard/PGM.h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/shard/PGM.h b/include/shard/PGM.h
index 73688ae..20bdbf2 100644
--- a/include/shard/PGM.h
+++ b/include/shard/PGM.h
@@ -342,12 +342,20 @@ public:
     }
 
     static std::vector<R> merge(std::vector<std::vector<R>> &results) {
+        size_t total = 0;
+        for (size_t i=0; i<results.size(); i++) {
+            total += results[i].size();
+        }
+
+        if (total == 0) {
+            return std::vector<R>();
+        }
+
         std::vector<R> output;
+        output.reserve(total);
 
         for (size_t i=0; i<results.size(); i++) {
-            for (size_t j=0; j<results[i].size(); j++) {
-                output.emplace_back(results[i][j]);
-            }
+            std::move(results[i].begin(), results[i].end(), std::back_inserter(output));
         }
 
         return output;
-- 
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