better ctf shuffle

Author: f3sch

Detectors/CTF/workflow/src/CTFReaderSpec.cxx

@@ -304,20 +304,22 @@ void CTFReaderSpec::openCTFFile(const std::string& flname)
       throw std::runtime_error(fmt::format("CTF tree in {} has 0 entries, skipping", flname));
     }
     if (mInput.shuffle) {
+      if (mInput.ctfIDs.empty()) {
+        int entries = mCTFTree->GetEntries();
+        if (mInput.maxTFs > 0) {
+          entries = std::min(entries, mInput.maxTFs);
+        }
+        if (mInput.maxTFsPerFile > 0) {
+          entries = std::min(entries, mInput.maxTFsPerFile);
+        }
+        mInput.ctfIDs.clear();
+        mInput.ctfIDs.resize(entries);
+        std::iota(mInput.ctfIDs.begin(), mInput.ctfIDs.end(), 0);
+      }
       std::random_device dev;
       std::mt19937 gen{dev()};
-      int entries = mCTFTree->GetEntries();
-      if (mInput.maxTFs > 0) {
-        entries = std::min(entries, mInput.maxTFs);
-      }
-      if (mInput.maxTFsPerFile > 0) {
-        entries = std::min(entries, mInput.maxTFsPerFile);
-      }
-      mInput.ctfIDs.clear();
-      mInput.ctfIDs.resize(entries);
-      std::iota(mInput.ctfIDs.begin(), mInput.ctfIDs.end(), 0);
       std::shuffle(mInput.ctfIDs.begin(), mInput.ctfIDs.end(), gen);
-      LOGP(info, "will shuffle CTF entries in this order:");
+      LOGP(info, "will shuffle reading of CTF entries in this order:");
       for (int i{0}; i < (int)mInput.ctfIDs.size(); ++i) {
         LOGP(info, "\tTF {:02} -> {:02}", i, mInput.ctfIDs[i]);
       }