How to make Snapshot of RDataFrame that contains STL collections?

[kandrosov]

Hello,
I would like to select and store a subset of entries from the original big TTree that contains branches with STL collections. Here is an example of the code:

import ROOT
ROOT.gInterpreter.GenerateDictionary('vector<ROOT::Math::LorentzVector<ROOT::Math::PtEtaPhiM4D<float> > >')
df = ROOT.RDataFrame('events', 'data.root')
df = df.Filter(...)
df.Snapshot('events', 'filtered.root', '.*')

When I am trying to run it I’m getting errors similar to this one:

Error in <TTree::Branch>: The class requested (vector<ROOT::Math::LorentzVector<ROOT::Math::PtEtaPhiM4D<float> > >) for the branch "lep_p4" is an instance of an stl collection and does not have a compiled CollectionProxy. Please generate the dictionary for this collection (vector<ROOT::Math::LorentzVector<ROOT::Math::PtEtaPhiM4D<float> > >) to avoid to write corrupted data.

So, it seems that ROOT.gInterpreter.GenerateDictionary does not make any effect. Could you, please, suggest me how to solve this error?

Thank you!

Cheers,
Konstantin.

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ROOT Version: 6.18/04
Platform: x86_64-slc6
Compiler: gcc8

[eguiraud]

Hi,
uhm I’m not sure why the GenerateDictionary call would not be picked up, maybe @pcanal knows. Here are other ways to generate dictionaries that you could try out.

Cheers,
Enrico

[kandrosov]

Hello Enrico,
thank you for the prompt reply and for the suggestion!
Indeed, using the other way to generate dictionaries helped.
Cheers,
Konstantin.

---

Here is a working solution for the reference.
Call ROOT.gInterpreter.ProcessLine('.L def.h+') instead of GenerateDictionary. And put pragma statement to generate dictionary into def.h:

#include <vector>
#include <Math/PtEtaPhiM4D.h>
#include <Math/LorentzVector.h>

#pragma link C++ class vector<ROOT::Math::LorentzVector<ROOT::Math::PtEtaPhiM4D<float> > >;