Plot quantity stored in a leaf

ROOT
1

Hi All,

How can I plot a quantity stored in a leaf of a root file by writing a macro?
Moreover, could you please point me to a basic guide with many examples of macros.

Thank you for your time.

2

If you speak about “leaf” it means you are using a TTree or a TNuple .
To draw a tree variable, v, simply do:

tree->Draw("v");

You can find examples here: ROOT: Tree tutorials

1 Like
4

Hi Couet,
Thank you for your message.
I tried the following macro:

void mymacro () {
TFile *f = new TFile(“myrootfile.root”,“READ”);
f->Draw(“leafname”);
}

It gives no error but draws nothing. I would like to get a plot of the quantity stored in leafname.
Thank you for your time.

5

Hello John1,

Here, f is a TFile not a tree. It will work when there is tree instead of f and leafname is one of its leaf, for sure.

6

Hi NepNeeraj,
Could you please be more explicit?
If the name of my file is myrootfile.root, the name of the branch “branchname”, and the name of the leaf “leafname”, how should I proceed with a macro to plot the quantity stored in the leaf?
Thank you for your help.

7

I guess, your branchname is under tree, try this,

void mymacro(){
TFile *f = new TFile(“myrootfile.root”);
tree->Draw(“branchname.leafname”);
}

in terminal load, .x mymacro.C, it should at least give a histogram filling the leaf contents.

8

It gives:

bash: .x: command not found

and,

error: use of undeclared identifier ‘tree’

9

. x is not a shell command. From the bash shell you can type:

$ root mymacro.C

or you can enter root just typing root and then type .x mymacro.C

$ root
....
root[0] .x mymacro.C

Now in your macro itself you attach the ROOT file myrootfile.root via the class TFile. That’s fine but as @NepNeeraj said that’s not your tree. The tree is inside this file. If you do not know the name of the tree you can type:

root [0] TFile *f = new TFile(“myrootfile.root”);
root [1] f->ls()

This will list the content or you file and you will see the name of the tree (if it exist) you want to access.

10

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