[PWGLF] enabled efficient and scoped analysis per collision (#12050)

Author: alcaliva

PWGLF/Tasks/Strangeness/strangenessInJets.cxx

@@ -972,6 +972,11 @@ struct StrangenessInJets {
   }
   PROCESS_SWITCH(StrangenessInJets, processData, "Process data", true);
 
+  Preslice<aod::V0Datas> perCollisionV0 = o2::aod::v0data::collisionId;
+  Preslice<aod::CascDataExt> perCollisionCasc = o2::aod::cascade::collisionId;
+  Preslice<aod::McParticles> perMCCollision = o2::aod::mcparticle::mcCollisionId;
+  Preslice<DaughterTracksMC> perCollisionTrk = o2::aod::track::collisionId;
+
   // Generated MC events
   void processMCgenerated(aod::McCollisions const& collisions, aod::McParticles const& mcParticles)
   {
@@ -994,9 +999,12 @@ struct StrangenessInJets {
       // Multiplicity of generated event
       double genMultiplicity = 0.0;
 
+      // MC particles per collision
+      auto mcParticlesPerColl = mcParticles.sliceBy(perMCCollision, collision.globalIndex());
+
       // Loop over all MC particles and select physical primaries within acceptance
       std::vector<fastjet::PseudoJet> fjParticles;
-      for (const auto& particle : mcParticles) {
+      for (const auto& particle : mcParticlesPerColl) {
         if (!particle.isPhysicalPrimary())
           continue;
         double minPtParticle = 0.1;
@@ -1048,7 +1056,7 @@ struct StrangenessInJets {
         getPerpendicularAxis(jetAxis, ueAxis2, -1);
 
         // Loop over MC particles
-        for (const auto& particle : mcParticles) {
+        for (const auto& particle : mcParticlesPerColl) {
           if (!particle.isPhysicalPrimary())
             continue;
           double minPtParticle = 0.1;
@@ -1152,9 +1160,14 @@ struct StrangenessInJets {
       // Event multiplicity
       const float multiplicity = collision.centFT0M();
 
+      // Number of V0 and cascades per collision
+      auto v0sPerColl = fullV0s.sliceBy(perCollisionV0, collision.globalIndex());
+      auto cascPerColl = Cascades.sliceBy(perCollisionCasc, collision.globalIndex());
+      auto tracksPerColl = mcTracks.sliceBy(perCollisionTrk, collision.globalIndex());
+
       // Loop over reconstructed tracks
       std::vector<fastjet::PseudoJet> fjParticles;
-      for (auto const& track : mcTracks) {
+      for (auto const& track : tracksPerColl) {
         if (!passedTrackSelectionForJetReconstruction(track))
           continue;
 
@@ -1217,7 +1230,7 @@ struct StrangenessInJets {
 
         // V0 particles
         if (particleOfInterest == Option::kV0Particles) {
-          for (const auto& v0 : fullV0s) {
+          for (const auto& v0 : v0sPerColl) {
             const auto& pos = v0.posTrack_as<DaughterTracksMC>();
             const auto& neg = v0.negTrack_as<DaughterTracksMC>();
             TVector3 v0dir(v0.px(), v0.py(), v0.pz());
@@ -1316,7 +1329,7 @@ struct StrangenessInJets {
 
         // Cascades
         if (particleOfInterest == Option::kCascades) {
-          for (const auto& casc : Cascades) {
+          for (const auto& casc : cascPerColl) {
             auto bach = casc.bachelor_as<DaughterTracksMC>();
             auto pos = casc.posTrack_as<DaughterTracksMC>();
             auto neg = casc.negTrack_as<DaughterTracksMC>();