Reading history inside a TTree

[PPierre]

Holà,

I would need some help about reading an histogram which is a leaf of a TBranch (‘depositedEnergy’) on a TTree.
I would like to get the standard deviation. Here is a snippet of my C++ code inside a macro :

TFile f("myROOTfile");  //open the root file
    Double_t temp; // define the variables to hold the read values
    TTree *T = (TTree*)f.Get("Detector_PV_Detector_PV_depositedEnergy");  //open my tree
    T->SetBranchAddress("depositedEnergy",&depositedEnergy); //branch name + address of the variable
    cout << T->GetStdDev() << "      " << T->GetEntries() << endl;

Without any surprise I have an error message saying that “T” is a TTree and the method GetStdDev() doesn’t belong to that class (you can only apply it to a TH1F).

How should one use the Tree->GetHistogram() method please ?

(Would have you proceed another way ?)

Thanks !

_ROOT Version: 6.10
_Platform: macOS

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[bellenot]

Try something like this:

TFile *f = TFile::Open("myROOTfile");
TTree *t = (TTree *)f->Get("Detector_PV_Detector_PV_depositedEnergy");
t->Draw("depositedEnergy>>h");
h->GetStdDev();

[PPierre]

Thanks ! How h should be declare though ?

[bellenot]

TH1F *h = (TH1F *)gDirectory->Get("h");
For example:

root [0] auto f = TFile::Open("data.root");
root [1] TTree *t = (TTree *)f->Get("TreeS");
root [2] t->Draw("var0>>h");
Info in <TCanvas::MakeDefCanvas>:  created default TCanvas with name c1
root [3] TH1F *h = (TH1F *)gDirectory->Get("h");
root [4] h->GetStdDev()
(double) 0.54692870
root [6]

[PPierre]

Ok I get it, works for me. Thanks !

[bellenot]

Or even simpler:

ROOT::RDataFrame df("Detector_PV_Detector_PV_depositedEnergy", "myROOTfile");
auto h = df.Histo1D("depositedEnergy");
cout << h->GetStdDev() << endl;

[PPierre]

Ok I will try you last answer, knowing that I will write that in a loop, I would like to avoid drawing anything.

PS :
Also similar to your first proposal :

T->Draw("depositedEnergy"); // stored in the current directory
TH1 *h = (TH1*)gPad->GetPrimitive("htemp");

[PPierre]

Should one use :

EnableImplicitMT()

in order to declare RDataFrame ?

[bellenot]

@PPierre

Also similar to your first proposal :

T->Draw("depositedEnergy"); // stored in the current directory
TH1 *h = (TH1*)gPad->GetPrimitive("htemp");

You’re right, but in my example you have control on the histogram variable name (e.g. if you have several ones) instead of htemp

[bellenot]

@PPierre

Should one use :

EnableImplicitMT()

in order to declare RDataFrame ?

Yes, if you want to use multiple threads

[PPierre]

AH ok sorry it’s not what I wanted to ask.
It 's just that I have that error message : error: no member named ‘RDataFrame’ in namespace ‘ROOT’ and I don’t know how to proceed ? I cannot find any header with that name…

#include"ROOT/RDataFrame.h"

fatal error: ‘ROOT/RDataFrame.h’ file not found

[bellenot]

Oh, OK, sorry, you’re using 6.10 and I think it’s too old. It has been introduced in 6.14, according to this post: RDataFrame, a modern tool to manipulate and analyze ROOT datasets