Add track selection to DL2

We train IPRNN with a track selection similar to IP3D. In DL2 there was previously no way to apply a track selection, so I've added it with this commit. For now there are two hardcoded track selections:

• ALL: select all the tracks.
• IP3D_2018: what we were using in IP3D around the end of 2018.

As with many of the DL2 input behaviors, the track order is currently determined via regexes that parse the NN file. The list of regular expressions is currently hardcoded in DL2HighLevel.cxx.

PhysicsAnalysis/JetTagging/FlavorTagDiscriminants/FlavorTagDiscriminants/DL2.h

@@ -31,6 +31,7 @@ namespace FlavorTagDiscriminants {
 
   enum class EDMType {UCHAR, INT, FLOAT, DOUBLE, CUSTOM_GETTER};
   enum class SortOrder {ABS_D0_SIGNIFICANCE_DESCENDING, PT_DESCENDING};
+  enum class TrackSelection {ALL, IP3D_2018};
 
   // Structures to define DL2 input.
   //
@@ -49,6 +50,7 @@ namespace FlavorTagDiscriminants {
   {
     std::string name;
     SortOrder order;
+    TrackSelection selection;
     std::vector<DL2TrackInputConfig> inputs;
   };
 
@@ -57,9 +59,13 @@ namespace FlavorTagDiscriminants {
   //
   // We define a few structures to map variable names to type, default
   // value, etc. These are only used by the high level interface.
+  //
+  // TODO: move this stuff into another file, i.e. either DL2HighLevel
+  // or some utility file that is also included in DL2HighLevel.cxx
   typedef std::vector<std::pair<std::regex, EDMType> > TypeRegexes;
   typedef std::vector<std::pair<std::regex, std::string> > StringRegexes;
   typedef std::vector<std::pair<std::regex, SortOrder> > SortRegexes;
+  typedef std::vector<std::pair<std::regex, TrackSelection> > TrkSelRegexes;
 
   // Function to map the regular expressions + the list of inputs to a
   // list of variable configurations.
@@ -70,7 +76,8 @@ namespace FlavorTagDiscriminants {
   std::vector<DL2TrackSequenceConfig> get_track_input_config(
     const std::vector<std::pair<std::string, std::vector<std::string>>>& names,
     const TypeRegexes& type_regexes,
-    const SortRegexes& sort_regexes);
+    const SortRegexes& sort_regexes,
+    const TrkSelRegexes& select_regexes);
 
 
   // _____________________________________________________________________
@@ -84,6 +91,7 @@ namespace FlavorTagDiscriminants {
     typedef std::vector<const xAOD::TrackParticle*> Tracks;
     typedef std::function<bool(const xAOD::TrackParticle*,
                                const xAOD::TrackParticle*)> TrackSort;
+    typedef std::function<bool(const xAOD::TrackParticle*)> TrackSelect;
 
     // getter functions
     typedef std::function<NamedVar(const Jet&)> Getter;
@@ -118,18 +126,23 @@ namespace FlavorTagDiscriminants {
       }
     };
 
+    // The track getter is responsible for getting the tracks from the
+    // jet applying a selection, and then sorting the tracks.
     class TrackGetter
     {
     public:
-      TrackGetter(SortOrder);
+      TrackGetter(SortOrder, TrackSelection);
       Tracks operator()(const xAOD::Jet& jet) const;
     private:
       typedef SG::AuxElement AE;
       typedef std::vector<ElementLink<xAOD::TrackParticleContainer>> TrackLinks;
       AE::ConstAccessor<TrackLinks> m_track_associator;
       TrackSort m_sort_function;
+      TrackSelect m_select_function;
     };
 
+    // The sequence getter takes in tracks and calculates arrays of
+    // values which are better suited for inputs to the NNs
     template <typename T>
     class SequenceGetter
     {
@@ -160,7 +173,7 @@ namespace FlavorTagDiscriminants {
     void decorate(const xAOD::Jet& jet) const;
   private:
     struct TrackSequenceGetter {
-      TrackSequenceGetter(SortOrder);
+      TrackSequenceGetter(SortOrder, TrackSelection);
       std::string name;
       internal::TrackGetter getter;
       std::vector<internal::SeqGetter> sequence_getters;
@@ -180,6 +193,7 @@ namespace FlavorTagDiscriminants {
   namespace internal {
     Getter get_filler(std::string name, EDMType, std::string default_flag);
     TrackSort get_track_sort(SortOrder);
+    TrackSelect get_track_select(TrackSelection);
     SeqGetter get_seq_getter(const DL2TrackInputConfig&);
   }
 }