How to project to histogram using a variable with whitespace

ROOT
1

I want to create a histogram of a variable. I want to collect in this histogram all of the values of this variable that are in events that have a certain flag existing. This flag is “e MET jets”, as shown in the following image:

Given that the variables tree is “nominal”, I have in mind something like the following, using the method TTree::Project():

h1 = new TH1D("h1", "h1", 10, 0, 200000)
nominal->Project("h1", "e MET jets")
h1->Draw()

When I try to specify the flag name with whitespace, I get the following error:

Error in <TTreeFormula::Compile>:  Bad numerical expression : "eMETjets"
Info in <TSelectorDraw::AbortProcess>: Variable compilation failed: {e MET jets,}
(Long64_t) -1

When I try to specify the flag name with escaped whitespace (“e\ MET\ jets”), I get the following error:

ROOT_prompt_30:1:31: warning: unknown escape sequence '\ '
      [-Wunknown-escape-sequence]
nominal->Project("h1", "e\ MET\ jets")
                              ^~
Error in <TTreeFormula::Compile>:  Bad numerical expression : "eMETjets"
Info in <TSelectorDraw::AbortProcess>: Variable compilation failed: {e MET jets,}
(Long64_t) -1

So,
[ul]
Is there some good documentation on the use of the method TTree::Project()?
How should I specify as a condition of the projection the existence of a variable for the event?
How should I specify the name of the variable, given that it contains whitespace?
[/ul]

2

TTree variables should be compliant with the C++ variable names coding rules i.e.: they should not contains special characters like % # $ etc … or white spaces, they should not be numbers or start with a number. If you do not follow these rules you will not be able to generate proper C++ code when you do TTree::MakeSelector(). In your case the best is to regenerate your TTree with proper variable names.

3

Ok, thanks for your help on that. Would you happen to know if there is some documentation on the workings of the Project method and other associated concepts? Some examples would be nice.

4

root.cern.ch/root/html/TTree.html