Add a utility function to return objects index inside a provided LCCo…

…llection

src/cpp/CMakeLists.txt

@@ -121,6 +121,7 @@ SET( LCIO_UTIL_SRCS
   ./src/UTIL/ILDConf.cc
   ./src/UTIL/ProcessFlag.cc
   ./src/UTIL/TrackTools.cc
+  ./src/UTIL/LCCollectionTools.cc
 )
 
 SET( LCIO_MT_SRCS

src/cpp/include/UTIL/LCCollectionTools.h

@@ -0,0 +1,15 @@
+#ifndef UTIL_LCCollectionTools_H
+#define UTIL_LCCollectionTools_H 1
+
+#include "EVENT/LCObject.h"
+#include "EVENT/LCCollection.h"
+
+namespace UTIL{
+    /** Extract object index inside a given LCCollection. If object is not found, return -1.
+    * @author Bohdan Dudar
+    * @version August 2022
+    */
+    int getElementIndex(const EVENT::LCObject* item, EVENT::LCCollection* collection);
+}
+
+#endif

src/cpp/src/UTIL/LCCollectionTools.cc

@@ -0,0 +1,10 @@
+#include "UTIL/LCCollectionTools.h"
+
+namespace UTIL{
+    int getElementIndex(const EVENT::LCObject* item, EVENT::LCCollection* collection){
+        for(int i=0; i < collection->getNumberOfElements(); ++i){
+            if ( item == collection->getElementAt(i) ) return i;
+        }
+        return -1;
+    }
+}