auto histo_leading = df.Filter("jet_pt.size() > 0")
.Define("leading_jet_pt", "jet_pt[0]")
.Histo1D("leading_jet_pt");
and similarly for the sub-leading jet.
As for why SetBranchAddress did not work for you, I think with TTree you need to read float arrays into raw arrays, i.e. something like Float_t *arr = nullptr; tree.SetBranchAddress("jet_pt", &arr);, but @pcanal can cmment with more authority.
Cheers,
Enrico
Dear Enrico,
Thanks a lot for your quick reply!
Yes! I just checked out the RDataFrame, and indeed the type of that branch is ROOT::VecOps::RVec<Float_t>. I will now try to link it to a local ROOT::VecOps::RVec<Float_t> and this time it should work.
And thanks for pointing out the possibility to use RDataFrame to handle the data quickly, this sounds like a columnar method. Unfortunately, I have some other operations need to do inside each event, and a loop still seems to be the most straightforward way to deal with:)
Thanks again for your kind help!
Best regards,
Sebastian
Xuli:
I will now try to link it to a local ROOT::VecOps::RVec<Float_t> and this time it should work.
Ah, I think RDataFrame is hiding the fact that this is just a Float_t* raw array (that RDataFrame reads as an RVec<Float_t> to be helpful). Using a raw C-style array is still your best bet, I think.
(As an aside, note that RDataFrame has zero problems with operations on nested collections.)
Dear Enrico,
Hmm, you are right, I think after loading the tree into RDataFrame, the branch is transformed into ROOT::VecOps::RVec<Float_t>…
I’ve tried a bit, and here is what I found:
TTree tree = (TTree)file->Get(“Events”);
Float_t *pt = NULL;
tree->SetBranchAddress(“Jet_pt”,&pt);
tree->GetEntry(0);
cout<at(0)<<endl;
Resulted in :error: member reference base type ‘Float_t’ (aka ‘float’) is not a structure or union
TTree tree = (TTree)file->Get(“Events”);
Float_t pt;
tree->SetBranchAddress(“Jet_pt”,&pt);
tree->GetEntry(0);
cout<<pt<<endl;
Resulted in a single value: 227.625
but no matter how I try I still can not get the corresponding array…
Thanks a lot!
Sebastian
From the “tree->Print()” output in your original post above (for a variable size array, you should see there something like “Jet_pt[nJet]”) and then from your very last trial (the one that returned 227.625), it is clear that the “Jet_pt” is a single ordinary “Float_t” value.
If you don’t know how to deal with your tree, see how various flavours of automatically generated “analysis skeletons” deal with it.
Jet_pt in NanoAODs should really be an array, and RDF agrees. I think you can read the first element of a C-style array as if it was a simple double.
EDIT:
as a test, could you please try running the following:
ROOT::RDataFrame df("Events", "nanoaodfile.root");
df.Filter("cout << jet_pt.size() << endl; return true;").Count().GetValue();
It should print the array sizes to screen. You can do the same to print the values.
So Jet_pt branch is indeed array-like. I tried to access them using:
Float_t jet_pt_arr;
eventTree->SetBranchAddress(“Jet_pt”, &jet_pt_arr);
eventTree->GetEntry(ientry);
cout<<(&jet_pt_arr)[i]<<endl;
It seemed to be working at first (can print several reasonable values), but later on when it went to higher indices (but is still within nJet), it started printing near-zero float values (0 in the float case). I also tried to do the histogram of pt of all the jets, and the resulted plot is different from what I got from ROOT Object Browser. So I guess &jet_pt_arr is not pointed to the correct beginning of the Jet_pt array… Very confusing…
Thanks a lot!
Best,
Sebastian
Alright. The automatically generated analysis skeletons suggested by @Wile_E_Coyote might show the right syntax to access those branches with raw TTree.
Otherwise we need @pcanal.
Cheers,
Enrico
I tried another recipe which works:
Float_t *jet_pt_arr = new Float_t;
eventTree->SetBranchAddress(“Jet_pt”, jet_pt_arr);
eventTree->GetEntry(ientry);
cout<<jet_pt_arr[i]<<endl;
However, it seems the declaration of
Float_t *jet_pt_arr = new Float_t;
resulted in some weird behavior of ROOT.
Here is a working example, if you could find a small CMS nanoAOD file (nanoAOD.root) to use:
void debug() {
UInt_t count0=0;
//=================== Chunk 1 ==============================
TString outfilename = TString("study.root");
TFile *outFile = new TFile(outfilename,"RECREATE");
TTree *outTree = new TTree("Events","Events");
//=========================================================
UInt_t njet = -999;
Float_t *jet_pt_arr = new Float_t;
// loop through files
TTree* eventTree = 0;
std::vector<TString> file_list;
file_list.push_back("nanoAOD.root");
for(int ifile=0; ifile<file_list.size(); ifile++){
TFile *infile = TFile::Open(file_list.at(ifile),"READ");
assert(infile);
// Access Event Tree
eventTree = (TTree*)infile->Get("Events");
assert(eventTree);
eventTree->SetBranchAddress("nJet", &njet);
eventTree->SetBranchAddress("Jet_pt", jet_pt_arr);
for(UInt_t ientry=0; ientry<eventTree->GetEntries(); ientry++){
// for(UInt_t ientry=0; ientry<100; ientry++){
count0++;
eventTree->GetEntry(ientry);
cout<<jet_pt_arr[i]<<endl;
}// End of event loop
infile->Close();
}// End of file loop
cout<<"Number of events processed: "<<count0<<endl;
// =================== Chunk 2 ==============================
outFile->cd();
outFile->Write();
outFile->Close();
// =========================================================
So occasionally (around 6-7 times out of 10 runs with the same code and sample nanoAOD.root), when quitting from ROOT, I got
*** Error in `JetAna/bin/root.exe': double free or corruption (out): 0x000056383c64abc0 ***
or segment violation. However, if we comment out this line:
eventTree->GetEntry(ientry);
or comment out chunk 1 and chunk 2 labeled in the example, the script would work without any problem…
I am a bit confused since I am not seeing why the declaration of output file and output tree would interfere with eventTree->GetEntry(ientry); and screw up the process.
I am sorry if this is running away from my original question, but I would still like to seek for some advice here:)
Thanks a lot for your kind help!
Best regards,
Sebastian
Dear Enrico, and @Wile_E_Coyote
Thanks a lot for your suggestions!
So it turned out the TTreeReader is much easier to use in this case, as being used in the method of eventTree->MakeClass() 
Thanks again for your kind help!
Best regards,
Sebastian
