From d53ad1623c6aa18034cb21b0901b8694e6c2cebd Mon Sep 17 00:00:00 2001
From: Sandro Wenzel <sandro.wenzel@cern.ch>
Date: Mon, 23 Mar 2026 13:02:21 +0100
Subject: [PATCH] aodMerger: Special option to merge only folders of the same
 name

Adding a special `merge-by-name` option which asks the merger only
to merge together dataframe folders of the same name.

This is needed only in special situations where we want to enfore the output
structure of the AOD to be the same as that of a reference (data) AOD.
An example is MC-DATA embedding.
---
 Framework/AODMerger/src/aodMerger.cxx | 28 ++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/Framework/AODMerger/src/aodMerger.cxx b/Framework/AODMerger/src/aodMerger.cxx
index 3ea45e84a39e0..53655a16584c6 100644
--- a/Framework/AODMerger/src/aodMerger.cxx
+++ b/Framework/AODMerger/src/aodMerger.cxx
@@ -38,6 +38,7 @@ int main(int argc, char* argv[])
   long maxDirSize = 100000000;
   bool skipNonExistingFiles = false;
   bool skipParentFilesList = false;
+  bool mergeByName = false;
   int verbosity = 2;
   int exitCode = 0; // 0: success, >0: failure
   int compression = 505;
@@ -50,6 +51,7 @@ int main(int argc, char* argv[])
     {"skip-non-existing-files", no_argument, nullptr, 3},
     {"skip-parent-files-list", no_argument, nullptr, 4},
     {"compression", required_argument, nullptr, 5},
+    {"merge-by-name", no_argument, nullptr, 6},
     {"verbosity", required_argument, nullptr, 'v'},
     {"help", no_argument, nullptr, 'h'},
     {nullptr, 0, nullptr, 0}};
@@ -70,6 +72,8 @@ int main(int argc, char* argv[])
       skipParentFilesList = true;
     } else if (c == 5) {
       compression = atoi(optarg);
+    } else if (c == 6) {
+      mergeByName = true;
     } else if (c == 'v') {
       verbosity = atoi(optarg);
     } else if (c == 'h') {
@@ -80,6 +84,7 @@ int main(int argc, char* argv[])
       printf("  --skip-non-existing-files    Flag to allow skipping of non-existing files in the input list.\n");
       printf("  --skip-parent-files-list     Flag to allow skipping the merging of the parent files list.\n");
       printf("  --compression <root compression id>  Compression algorithm / level to use (default: %d)\n", compression);
+      printf("  --merge-by-name              Only merge TTrees from folders with the same name.\n");
       printf("  --verbosity <flag>           Verbosity of output (default: %d).\n", verbosity);
       return -1;
     } else {
@@ -94,6 +99,9 @@ int main(int argc, char* argv[])
   if (skipNonExistingFiles) {
     printf("  WARNING: Skipping non-existing files.\n");
   }
+  if (mergeByName) {
+    printf("  Merging only folders with the same name.\n");
+  }
 
   std::map<std::string, TTree*> trees;
   std::map<std::string, uint64_t> sizeCompressed;
@@ -182,6 +190,24 @@ int main(int argc, char* argv[])
 
       auto dfName = ((TObjString*)key1)->GetString().Data();
 
+      // If merge-by-name is active, flush accumulated trees when the folder name changes
+      if (mergeByName && outputDir && std::string(outputDir->GetName()) != std::string(dfName)) {
+        if (verbosity > 0) {
+          printf("Folder name changed: closing folder %s.\n", outputDir->GetName());
+        }
+        for (auto const& tree : trees) {
+          outputDir->cd();
+          tree.second->Write();
+          sizeCompressed[tree.first] += tree.second->GetZipBytes();
+          sizeUncompressed[tree.first] += tree.second->GetTotBytes();
+          delete tree.second;
+        }
+        outputDir = nullptr;
+        trees.clear();
+        offsets.clear();
+        mergedDFs = 0;
+      }
+
       if (verbosity > 0) {
         printf("  Processing folder %s\n", dfName);
       }
@@ -462,4 +488,4 @@ int main(int argc, char* argv[])
   printf("\n");
 
   return exitCode;
-}
+}
\ No newline at end of file