Create an histogram with a txt file

[rrapo]

ROOT Version: 6.26/02
Platform: macOs
_Compiler: Xcode

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Hi everyone.
i am sorry for my bad English, I hope you will forgive me.

i have some little issues with creating a histogram: I already tried to look for something useful in the previous questions and answers, but I was a little confused.

I need to do a histogram which contains the x-values (first column of the txt file I will share here) and how many times a software has seen the y-values (second column).
how can I make a decent histogram with these data…
is it possibile with TH1F? I need then to do some fit on this histogram…

here I paste the txt file
spettrofotometro_nuovo.txt (46.4 KB)

second ps: I already succeeded in doing a graph considering the first column as a x-value and the second one as a y- value (I used them as points, but I’d like to have an histogram, since in the graph I needed to introduce the errors of the measures…)

I hope you can help me…
thanks for spending your time on answering for this question

[Wile_E_Coyote]

You can create a TGraphErrors, e.g.:
TGraphErrors *g = new TGraphErrors("spettrofotometro_nuovo.txt", "%lg %lg"); // read only 2 first columns into X,Y

Afterward, you can simply “add” any errors you need, using the TGraphErrors::SetPointError method.

[rrapo]

hi! thank you for the answer!
i am sorry, but I will bother you just a bit more

I already did this (and this does give me no issues), but this treats the x and y data as points, doesn’t it?

To be honest, I am pretty satisfied with this type of graph, since I can finish my data analysis, but I may need to do a histogram with (the y values are supposed to represent how many times the x-value appeared to the software which was used for the measure) just to satisfy my teacher’s desire…

is it possibile? if it is, could you tell me?

ps: I can, eventually, split the columns of the txt file and make two different txt files, but I don’t know how to make root generate a histogram with the frequency of events;

thank you for your time spent here!

[Wile_E_Coyote]

In the posts given below, you can find examples of how to create a histogram from a graph.

Facing Problem while fitting

The first parameter of “gaus” is the “peak’s height” while the first parameter of “gausn” is the “peak’s area”. In both cases, the second parameter is the “peak’s mean” (i.e. the “peak’s position”). { TGraph *g = new TGraph("eu_gu_1.dat"); // g->Sort(); // just a precaution TF1 *f1 = new TF1("f1", "gausn(0) + pol1(3)", 400., 435.); // linear background f1->SetParameters(14000., 415., 2., 0., 0.); g->Fit("f1", "BR+"); TF1 *f2 = new TF1("f2", "gausn(0) + pol1(3)", 1160., 1200.); f2…

Problem in fitting (in function!)

{ TGraphErrors *g = new TGraphErrors("data.txt", "%lg %lg %lg"); // g->Sort(); // just a precaution Int_t n = g->GetN(); Double_t *x = new Double_t[(n + 1)]; x[0] = (3.0 * g->GetX()[0] - g->GetX()[1]) / 2.0; x[n] = (3.0 * g->GetX()[(n - 1)] - g->GetX()[(n - 2)]) / 2.0; for (Int_t i = 1; i < n; i++) { x[i] = (g->GetX()[(i - 1)] + g->GetX()[i]) / 2.0; } TH1D *h = new TH1D("h", "spectrum;x-value;#counts", n, x); for (Int_t i = 0; i < n; i++) { h->SetBinContent(i + 1, g->Ge…

[rrapo]

Thank you so much!

i will make you one more question, which is the most stupid, but it’s making my brain implode (I don’t know why: how do I fill the histogram? (if it is h->FillN(…) it’s not working)

[Wile_E_Coyote]

TH1

[rrapo]

I am sorry for the question, this one was too stupid
i owe you a debt of gratitude, thank you! have a nice day!