Accessing data from Tree

[pure]

Hello Rooters
I have a root file and I want to read the leaf values and show them on the screen. This is a screenshot of my tree:

could anyone give a hint?

[Wile_E_Coyote]

Header files for Trees

“Most recent” documentation about how to generate and use an “analysis skeleton”: TTree::MakeClass (see also “ROOT User’s Guide” → “Trees” → “Using TTree::MakeClass”) TTree::MakeSelector (see also “ROOT Primer” → “File I/O and Parallel Analysis” → “N-tuples in ROOT” → “For the advanced user: Processing trees with a selector script” and “ROOT User’s Guide” → “Trees” → “Using TTree::MakeSelector” and “ROOT User’s Guide” → “Example Analysis”) TTree::MakeProxy ROOT::RDataFrame (uses the T…

[eguiraud]

Hi,
clicking on the name of a leaf shows its values in a histogram, is that what you are looking for?

To print out all the values, you can open the ROOT terminal and use TTree::Scan (see here).

Cheers,
Enrico

[pure]

Thanks. I know, but I want another way to do this, because I want then choose some of the values.

[eguiraud]

See @Wile_E_Coyote’s suggestion for one way to programmatically loop over TTree data. Here some other ways to loop over TTree data are described.

Cheers,
Enrico

[pure]

Thank you very much.

[pure]

Hello again

I have a branch called Particle and in that branch there is a leaf called Particle.spin. I want to make a constraint on the value of the leaf to select some special events. I use this condition:

if(Particle.Spin== 1)

but I get this error:

Error: Symbol Particle is not defined in current scope (tmpfile)(7)
Error: Failed to evaluate Particle.Spin

what is wrong with symbol Particle?

[eguiraud]

Hi,
I guess you never declared a variable called Particle.
Please check the links we shared and the TTree tutorials for actual code that you can use as a starting point.

Cheers,
Enrico

[pure]

what do you mean by declaring variable Particle?

[eguiraud]

In both C++ and python you have to declare/define a variable before using it. For example,

int x = 42;
if (x == 1) {
  ...
}

If the definition of x in the first line was not present, you would probably get a similar error saying Symbol x is not defined in current scope. In other words there is no object called Particle in your program. You have to define it (as a variable that TTree fills with the corresponding branch values) before you use it. For examples of how to define variables that are filled with TTree branch/leaf values, and how to tell TTree to actually fill those variables with values, see all the resources we linked.

Cheers,
Enrico

[pure]

Thank you very much.

[MihirPatel]

I am having the same problem as @pure is having. Can anyone please send a sample root file and a code for that?