Build a matrix or vector to store my data

ROOT
#1

Hello, there. I am a beginner for ROOT. I would like to know, if i have a dataset, how can i build a matrix or a vector to store the dataset and retrieve some of the data later in the same code? Thank you.

#2

Dear chlee91,

Could you please explain what do you mean by ‘without creating a ROOT file’ and why?
And what is your dataset made of? Integers, floats, objects of a given class?

G Ganis

#3

I have a set of data which is generated by random number generation, those are double_t numbers

#4

And is creating a root file to store data a must for this case?

#5

This is my code. Please let me know if there is something unclear. Thank you.

void random(Int_t nrEvents=80)
{
TRandom3 gRandom = new TRandom3();
TGraph g = new TGraph();
TVectorD arr(80);
Double_t y;
Double_t xmin = 700.0pow(10.0,6);
Double_t xmax = 800.0pow(10.0,6);
Double_t x = xmin;
Double_t dx = ((xmax-xmin)/nrEvents);
for (Int_t i=0;i<nrEvents;++i)
{
y = gRandom->Gaus(0.0, 1.0/(100.0));
cin>>arr[i];
g->SetPoint(i,xmin,y);
xmin=xmin+dx;
}
g->SetMarkerStyle(8);
g->Draw(“APL”);
}

#6

Dear chlee91,

You can use a TNtuple to store your vars. See examples under tutorial/tree

For 80 numbers no. But if you plan to have much larger numbers, it is advised.

G Ganis

#7

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