Creating histograms within a loop

ROOT
1

Hi all,
I’m trying to create a bunch of histograms whose names vary only slightly. They’re something like
histo1_neutron
histo2_neutron
…
histoN_neutron
histo1_gamma
histo2_gamma
…
histoN_gamma

Is there a way I can create these histograms (as pointers) in a for loop by looping over both the number (1,…,N) as well as the particles (neutron, gamma, …) e.g. by creating an array of the particles then looping over the entries in the array as well as the number 1 to N?

Thanks!

2

Hi,

certainly yes. This should get you started:

std::vector<TH1F*> myHistos; // you need to free this memory later
for (auto i : {1,2,3,4}) {
   for (auto part_name : {"neutron", "gamma", "whatever"}) {
      myHistos.emplace_back(new TH1F(Form("%s_%d", part_name, i),"yourtitle",64, -4, 4)); // binning made up
   }
}

I hope this help.
P

3

Thanks! How (and when) do i clear the memory?

4

Hi,

it really depends on you and when you need to free it. If you prefer an automatic management, i.e. by the cpp runtime, just use a vector<unique_ptr> :slight_smile:

Cheers,
P

5

Thank you so much for your help!