How to print (& fill histogram with) two branches that are array using TTreeReaderArray

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1

Hello all.

This topic is related to TTreeReaderArray.
The goal is to print out the values inside the branches (array) in the terminal.
I have branch “energy” and “time” as shown below.

root [19] OutputTree->Scan("det.energy_:det.time_","","",1000,78400)
***********************************************
*    Row   * Instance * det.energy_ * det.time_ *
***********************************************
*    78400 *        0 * 37.700216 * 1036.4219 *
*    78400 *        1 * 85.110013 * 1098.5080 *
*    78400 *        2 * 98.487813 * 1084.2928 *
*    78401 *        0 *           *           *
*    78402 *        0 * 72.195859 * 1036.3751 *
*    78402 *        1 * 35.378058 * 1084.2728 *
*    78402 *        2 * 56.932710 * 1107.9885 *
*    78402 *        3 * 39.948852 * 1074.6173 *
*    78403 *        0 *           *           *
*    78404 *        0 *           *           *
*    78405 *        0 *  103.0197 * -8.450341 *
*    78406 *        0 * 33.523407 * 1080.3913 *
*    78406 *        1 * 45.087502 * -0.422100 *
*    78406 *        2 * 56.645979 * 1099.3365 *
*    78407 *        0 * 11.311819 * 1081.0858 *
*    78408 *        0 *           *           *
*    78409 *        0 * 37.983352 * 1080.3177 *
*    78409 *        1 * 39.554136 * 1084.2923 *
*    78410 *        0 *           *           *

I access these branches using the TTreeReaderArray using the following code:

auto f = TFile::Open(filename);
TTreeReader r("OutputTree", f);
TTreeReaderArray<Double_t> v(r, "det.energy_");
TTreeReaderArray<Double_t> w(r, "det.time_");

while (r.Next()) 
{
for (auto &m : v)
printf("The energy is: %f\n", m);
}

//**How to print out the energy and time values together?**
//for (auto &n : w)    //time
//printf("The energy is: %f, the time is %f\n", m, n);

With the above line of code, I can successfully print out all the instances (array element) for the ‘energy’ branch as shown below:

The energy is: 37.700216
The energy is: 85.110013
The energy is: 98.487814
The energy is: 72.195860
The energy is: 35.378058
The energy is: 56.932710
The energy is: 39.948853
The energy is: 103.019700
The energy is: 33.523407
The energy is: 45.087503
The energy is: 56.645979
The energy is: 11.311820
The energy is: 37.983352
The energy is: 39.554136

Question: How can I print the values of the ‘time’ branch corresponding to the energy value?
That is I am looking to print in the following manner:

The energy is: 37.700216, the time is 1036.4219
The energy is: 85.110013, the time is 1098.5080
The energy is: 98.487814, the time is 1084.2928
The energy is: 72.195860, the time is 1036.3751
The energy is: 35.378058, the time is 1084.2728
The energy is: 56.932710, the time is 1107.9885
The energy is: 39.948853, the time is 1074.6173
The energy is: 103.019700, the time is -8.450341
The energy is: 33.523407, the time is 1080.3913
The energy is: 45.087503, the time is -0.422100
The energy is: 56.645979, the time is 1099.3365
The energy is: 11.311820, the time is 1081.0858
The energy is: 37.983352, the time is 1080.3177
The energy is: 39.554136, the time is 1084.2923

The final aim is to make (fill) a 2D histogram with these two branch values. How can I do it?
Also, if the same is possible with the RDataFrame, please guide on that too if possible.

ROOT Version: 6.26/10
Platform: Ubuntu 22.04.2 LTS

Thank you!

2

If they are the same size, you can simply do something like this:

for (auto i=0; i < v.GetSize(); ++i) {
   printf("The energy is: %f, the time is: %f\n", v[i], w[i]);
}

for (auto i=0; i < v.GetSize(); ++i) {
   h2->Fill(v[i], w[i]);
}

I’ll let @vpadulan give details for RDataFrame. Maybe something like:

auto file = TFile::Open(filename);
auto tree = file->Get<TTree>(treename);
ROOT::RDataFrame rdf(treename, filename);
auto h2 = rdf.Histo2D({"h2", "energy vs time", 100, 0., 100., 100, 0., 2000.}, "det.energy_", "det.time_");

(you can take a look at the RDataFrame tutorials)

1 Like
3

Thanks for the reply.

Yes, they have the same size.
Doing the above as recommended leads to: *** Break *** segmentation violation

4

Can you provide a minimal reproducer?

5

Sorry, I will have to make a minimal reproducer. As and when I make it, I will post it.
Thanks.

6

That’s usually an index out of range, like when the arrays are not the same size. So, add a check comparing the two sizes and print out (before the loop with printf("The energy is: %f, the time is: %f\n", v[i], w[i]) if they are different, you should see that message before the seg fault.

1 Like
7

Thanks for the reply.

I print the size with this:

#include <iostream>
#include <TTree.h>
#include <TFile.h>
#include <TTreeReader.h>
#include <TTreeReaderValue.h>
#include <TTreeReaderArray.h>

using namespace std;
void getsize()
{
auto f = TFile::Open("file.root");
TTreeReader r("OutputTree", f);
TTreeReaderArray<Double_t> v(r, "det.energy_");
TTreeReaderArray<Double_t> w(r, "det.time_");

   auto vsize = v.GetSize();
   auto wsize = w.GetSize();
   printf("v size is: %lu and w size is: %lu\n", vsize, wsize);

}

int main()
{
   getsize();
   return 0;
}

This also throws Seg fault.

8

You have to be inside the loop over r, of course; otherwise, how are you going to get any v or w?

1 Like
9

My mistake!

while(r.Next()){
           auto vsize = v.GetSize();
           auto wsize = w.GetSize();
           printf("v size is: %lu and w size is: %lu\n", vsize, wsize);}

This do return the same size for v and w!

10

Are you 100% sure? Do not check by eye, make the differences in the code and print a special message if they are different. If all are indeed equal, then continue as bellenot suggested.

1 Like
11

Thanks for the reply.
The Seg fault was due to the ‘not looping over r’. As suggested by you, I included it.
Now, Bellenot’s suggested lines work!

Thanks for the help!

1 Like