CollectionTree Issue

njeong · February 20, 2017, 1:58pm

Hello, ROOT Team

Now I am trying to read the variable like this.

{
   TChain chain("CollectionTree");
   chain.Add("2.root");
   TChain* ch;
   ch = &chain;
   Int_t entries=ch->GetEntries();
   cout<<endl;
   cout <<"entries: " << entries << endl;
   Float_t px;
   ch->SetBranchAddress("m_px",&px);
}

However I receive

entries: 2000
Error in <TChain::SetBranchAddress>: unknown branch -> m_px

I mean, I can receive the result “entries” but I can not receive the “px” value.

Help me

Thank you

-Nam

Danilo · February 20, 2017, 2:49pm

Hi Nam,

does the tree have a branch called “m_px”?

Cheers,
Danilo

njeong · February 20, 2017, 3:37pm

Dear Danilo

Please refer to the image. Could you help me?

-Nam

Danilo · February 20, 2017, 3:46pm

Hi,

the branch is then m_genParticles.m_px.
Did you consider using TTreeReader for analysing your chain?
root.cern.ch/doc/master/classTTreeReader.html

Cheers,
D

njeong · February 20, 2017, 4:34pm

Dear Danilo

Thank you for your reply.

However it is not working, I received same error:

entries: 2000
Error in <TChain::SetBranchAddress>: unknown branch -> m_genParticles.m_px

Do you have any idea?

-Nam

Danilo · February 20, 2017, 9:35pm

Before proceeding, why not moving to TTreeReader?

I did not notice that this is hanging from McEventCollection_p5_GEN_EVENT.
Please go for “McEventCollection_p5_GEN_EVENT.m_genParticles.m_px”.

Cheers,
D

Pepe_Le_Pew · February 20, 2017, 9:37pm

meenandm · November 27, 2023, 2:57pm

Hi,

Were you able to solve this as I am having the same error?

-meenandm

Danilo · December 5, 2023, 11:04am

Hi,

Welcome to the forum!
Could I suggest you open a new thread about the issue you are currently facing? A lot changed in ROOT (for good!) in the last 7y: we’ll be able to support your use case much better!

Cheers,
D