Get double entries count in TH1F

ROOT
1

Hi,

I have this issue.
The entries number given in a TH1F is double the number by using T->GetEntries(“CUT”) with same cuts applied. And the variable I plot in the TH1F is a number not array. I feel the number given by GetEntries should be the correct one. Can someone explain why the entries in histogram is bigger? Thanks!

Please provide the following information:

ROOT Version : 6.10.02
Platform, compiler (e.g. CentOS 7.3, gcc6.2): redhat

2

What is the “CUT” exactly?
How do you fill your histogram exactly?
(Basically, I think, from both approaches, you should get exactly the same number of entries.)

3

Here is the sentence related:

Double_t ntrack2 = T->GetEntries(beta+Ep+CK+VZ+trigger2+TRK2+ACC);
T->Draw(“L.s2.nthit”,beta+Ep+CK+VZ+trigger2+TRK2+ACC);

Those cuts (like beta, Ep) could be array or number.
The entries I see in the histogram is 2*ntrack2-1

4

Well, even if “L.s2.nthit” is just an ordinary value, but your “CUT” contains arrays then, I think, your histogram will be filled with this ordinary value as many times as there are elements in the arrays (which satisfy the selection).

5

Yeah. You’re right. After replacing the array with a number in “CUT”, those two entries are equal.
BTW, is there a simple way to make it fill the histogram only one time when an array is in the cut?

6

Well, see “Special functions and variables” in the TTree::Draw method description.

Maybe @couet has some better ideas.

7

You may also have a look at MakeSelector . Using it you have the full control.

8

Thank you all! I probably need some time to understand how to use it…

9
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10

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