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support index-based selection #502

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fce2d4a
support index-based selection
goblirsc Feb 16, 2026
8583260
fix a bug
goblirsc Feb 16, 2026
a1413ca
add one more helper
goblirsc Feb 16, 2026
24fc851
clang_format
goblirsc Feb 16, 2026
547242a
Revert "clang_format"
goblirsc Feb 17, 2026
67704a9
format fixes
goblirsc Feb 17, 2026
598ad75
the formatter strikes again
goblirsc Feb 20, 2026
4ff8c17
while (!CI_happy) run(formatter)
goblirsc Mar 2, 2026
1637717
yay
goblirsc Mar 4, 2026
7f736d2
document how to use clang format
goblirsc Mar 4, 2026
5dcba23
clarify readme
goblirsc Mar 4, 2026
609d6e4
move selByPredicate to Utils, add more doc
goblirsc Mar 16, 2026
6ff7a38
clang format
goblirsc Mar 16, 2026
f1fe587
Apply batched suggestions from code review
goblirsc Sep 3, 2026
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6 changes: 6 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -77,3 +77,9 @@ To apply formatting to a file:
```
clang-format -i -style=file /path/to/file.cpp
```
Note that this will reformat the entire file.
If you are preparing a PR, you can instead use
```
git clang-format --style=file $(git merge-base upstream/master HEAD)
```
to only format the lines you changed (otherwise you will reformat the entire file).

@kjvbrt kjvbrt Mar 4, 2026

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Thanks for figuring this out :)

Maybe (otherwise you will reformat the entire file) is a bit redundant, as the same information is a few lines above.

@kjvbrt kjvbrt Mar 4, 2026

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In any case, at some point we need to run formatter across the whole repository.

@goblirsc goblirsc Mar 4, 2026

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Fixed the description

@kjvbrt kjvbrt Mar 11, 2026

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Nice, maybe MR -> PR?

@goblirsc goblirsc Mar 16, 2026

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Fixed (caught a long-term gitlab user :) )

55 changes: 44 additions & 11 deletions analyzers/dataframe/FCCAnalyses/MCParticle.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
#define MCPARTICLE_ANALYZERS_H

#include <cmath>
#include <functional>
#include <vector>

#include "ROOT/RVec.hxx"
Expand Down Expand Up @@ -30,26 +31,49 @@ namespace MCParticle{
bool operator() (ROOT::VecOps::RVec<edm4hep::MCParticleData> in);
};

/// @brief Helper struct to select entries matching a certain predicate.

@kjvbrt kjvbrt Mar 4, 2026

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Could you also provide an example of usage?

@goblirsc goblirsc Mar 4, 2026

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Hi, sure - would you prefer this in the doxygen doc or on the PR?
The replacements for the selectors below this definition can serve as "inline" examples to refer to.

The general pattern is

struct mySelection: selByPredicate{
    mySelection(): selByPredicate(some_selection_function){}
};

Where some_selection_function is a function returning a "keep" decision for a given input object. Using lambda captures, the function can be configured with constructor arguments - for example, a configurable cut threshold.

This object can then be used to obtain a copy-vector of passed objects from an input object list, or a set of passing indices, or a set of passing element for each of a list of input index vectors.

The main motivation is that we save a lot of common boilerplate code when implementing selection functions (loop over containers, output allocation, copy operations, ...). The pattern also ensures that deep-copies are avoided where possible. We also gain the ability to apply the same selection functor transparently on index-based or copy-based selection logic, avoiding a need to duplicate logic if both are to be supported.

It would actually be more elegant to generalise this to a template consuming an arbitrary input object type, rather than being restricted to the MCParticleData class.

@kjvbrt kjvbrt Mar 11, 2026

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Nice explanation, I think having it in Doxygen would be the best. Would you also add an example how to use this when working with the dataframe in Python? I mean a snipped a user might write.

@goblirsc goblirsc Mar 16, 2026

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Added explanation for doxygen, including snippets. Also moved the selByPredicate to Utils, making it available more generally than before.

/// Supports two signatures - either a list of candidates is passed and a list
/// of accepted candidates returned, Or a list of indices in a vector of
/// candidates is passed and a list of accepted indices returned. The latter
/// is more compatible with index-based selection logic.
struct selByPredicate {
selByPredicate(
std::function<bool(const edm4hep::MCParticleData &)> thePredicate)
: m_predicate(thePredicate) {}
std::function<bool(const edm4hep::MCParticleData &)> m_predicate;
ROOT::VecOps::RVec<edm4hep::MCParticleData>
operator()(const ROOT::VecOps::RVec<edm4hep::MCParticleData> &in);
ROOT::VecOps::RVec<int>
operator()(const ROOT::VecOps::RVec<int> &indices,
const ROOT::VecOps::RVec<edm4hep::MCParticleData> &in);
ROOT::VecOps::RVec<ROOT::VecOps::RVec<int>>
operator()(const ROOT::VecOps::RVec<ROOT::VecOps::RVec<int>> &indices,
const ROOT::VecOps::RVec<edm4hep::MCParticleData> &in);
};

/// select MCParticles with transverse momentum greater than a minimum value [GeV]
struct sel_pt {
struct sel_pt : selByPredicate {
sel_pt(float arg_min_pt);
float m_min_pt = 20; //> transverse momentum threshold [GeV]
ROOT::VecOps::RVec<edm4hep::MCParticleData> operator() (ROOT::VecOps::RVec<edm4hep::MCParticleData> in);
};

/// select MCParticles with absolute pseudorapidity less than a max value
struct sel_eta : selByPredicate {
sel_eta(float arg_max_eta);
};

/// select MCParticles with their status
struct sel_genStatus {
struct sel_genStatus : selByPredicate {
sel_genStatus(int arg_status);
int m_status = 1; //> Generator status
ROOT::VecOps::RVec<edm4hep::MCParticleData> operator() (ROOT::VecOps::RVec<edm4hep::MCParticleData> in);
};

/// select MCParticles with their PDG id
struct sel_pdgID {
struct sel_pdgID : selByPredicate {
sel_pdgID(int arg_pdg, bool arg_chargeconjugate);
int m_pdg = 13;
bool m_chargeconjugate = true;
ROOT::VecOps::RVec<edm4hep::MCParticleData> operator() (ROOT::VecOps::RVec<edm4hep::MCParticleData> in);
};

/// select MCParticles with a non-zero charge
struct sel_charged : selByPredicate {
sel_charged();
};

/// get MC history tree for a given MCParticle index
Expand Down Expand Up @@ -116,7 +140,6 @@ namespace MCParticle{
ROOT::VecOps::RVec<edm4hep::MCParticleData> in ,
ROOT::VecOps::RVec<int> ind);


/// return the parent index of a given list of MC particles
ROOT::VecOps::RVec<int> get_parentid(ROOT::VecOps::RVec<int> mcind, ROOT::VecOps::RVec<edm4hep::MCParticleData> mc, ROOT::VecOps::RVec<int> parents);

Expand Down Expand Up @@ -210,6 +233,16 @@ namespace MCParticle{
/// return the list of stable particles from the decay of a mother particle, looking at the full decay chain recursively. i is the mother index in the Particle block
std::vector<int> get_list_of_stable_particles_from_decay( int i, ROOT::VecOps::RVec<edm4hep::MCParticleData> in, ROOT::VecOps::RVec<int> ind) ;

/// return the list of stable particles from the decays of a mother particle,
/// looking at the full decay chain recursively. i is the list of mother
/// indices to process in the Particle block. Will return a vector of vectors
/// - each vector is the set of children for one of the mothers in the input
/// vector
ROOT::VecOps::RVec<ROOT::VecOps::RVec<int>>
get_lists_of_stable_particles_from_decays(
ROOT::VecOps::RVec<int> i, ROOT::VecOps::RVec<edm4hep::MCParticleData> in,
ROOT::VecOps::RVec<int> ind);

/// return the list of particles from the decay of a mother particle. i is the mother index in the Particle block.
std::vector<int> get_list_of_particles_from_decay( int i,
ROOT::VecOps::RVec<edm4hep::MCParticleData> in,
Expand Down
44 changes: 38 additions & 6 deletions analyzers/dataframe/FCCAnalyses/ReconstructedParticle2MC.h
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Original file line number Diff line number Diff line change
Expand Up @@ -125,12 +125,44 @@ namespace ReconstructedParticle2MC{
ROOT::VecOps::RVec<edm4hep::ReconstructedParticleData> reco,
ROOT::VecOps::RVec<edm4hep::MCParticleData> mc) ;

/// select ReconstructedParticles matched to the (stable) MC particles whose indices are passed in a list
ROOT::VecOps::RVec<edm4hep::ReconstructedParticleData> selRP_matched_to_list( ROOT::VecOps::RVec<int> mcParticles_indices,
ROOT::VecOps::RVec<int> recind,
ROOT::VecOps::RVec<int> mcind,
ROOT::VecOps::RVec<edm4hep::ReconstructedParticleData> reco,
ROOT::VecOps::RVec<edm4hep::MCParticleData> mc) ;
/// select ReconstructedParticles matched to the MC particles whose indices
/// are passed in a list
/// @param mcParticles_indices indices of the MC particles to look up
/// @param recind: reco index component of the MCRecoAssociations
/// @param mcind: mc index component of the MCRecoAssociations
/// @param reco: full reco particle list (ReconstructedParticles)
/// @param mc: full mc particle list (Particles)
/// @param require_stable: if set to true, will only match stable particles.
/// @return List of ReconstructedParticle candidates with length corresponding
/// to the number of *stable* MC particles in the mcParticles_indices vector.
/// In presence of unstable particles, no 1:1 correspondence. For
/// non-reconstructed stable MC particles, a dummy particle will be inserted.
/// If 1:1 length correspondence is required, set require_stable to false.
ROOT::VecOps::RVec<edm4hep::ReconstructedParticleData> selRP_matched_to_list(
const ROOT::VecOps::RVec<int> &mcParticles_indices,
const ROOT::VecOps::RVec<int> &recind,
const ROOT::VecOps::RVec<int> &mcind,
const ROOT::VecOps::RVec<edm4hep::ReconstructedParticleData> &reco,
const ROOT::VecOps::RVec<edm4hep::MCParticleData> &mc,
bool require_stable = true);
/// select indices of ReconstructedParticles matched to the MC particles whose
/// indices are passed in a list
/// @param mcParticles_indices indices of the MC particles to look up
/// @param recind: reco index component of the MCRecoAssociations
/// @param mcind: mc index component of the MCRecoAssociations
/// @param mc: full mc particle list (Particles)
/// @param require_stable: if set to true, will only match stable particles.
/// @return List of ReconstructedParticle candidates with length corresponding
/// to the number of *stable* MC particles in the mcParticles_indices vector.
/// In presence of unstable particles, no 1:1 correspondence. For
/// non-reconstructed stable MC particles, a "-1" entry will be inserted. If
/// 1:1 length correspondence is required, set require_stable to false.
ROOT::VecOps::RVec<int> selRP_indices_matched_to_list(
const ROOT::VecOps::RVec<int> &mcParticles_indices,
const ROOT::VecOps::RVec<int> &recind,
const ROOT::VecOps::RVec<int> &mcind,
const ROOT::VecOps::RVec<edm4hep::MCParticleData> &mc,
bool require_stable = true);

/// return the index of the MC particle that is associated to a given track (via the track-reco association)
int getTrack2MC_index ( int track_index,
Expand Down
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