Make each tree of a file friends with each other

ROOT
1

I have a file with several trees: ch0, ch1, ch2,…ch23

In an steering file I give the user the possibility to make a selection of the events based on some variables ot the trees. My compiled code reads that string during execution and applies the selection. For example:

TString Selection=“ch0->Temp>0 && ch1->Voltage<200&&ch15->Amplitude>0.03”

Since the selection can refer to any tree in the file, I need to make each tree friends with each other. This means ch0 is friends of ch1,…ch23. Then ch1 is friends with ch0,ch2,…ch23, and so on.

The problem is that, if I make the above friendships, then a code like:

vector<TTree*> vtree;
vtree.push_back( ch0 ) ;vtree.push_back( ch1 ) ; //...I push_back here each of the Trees
vtree[0]->Draw( ">>myList" , Selection ) ;
TEventList *acclist = (TEventList*) gDirectory->Get("myList") ;
acclist->SetDirectory(0);

gets “infinitely” long.

Is there a smarter/faster way of doing this with trees?

Otherwise the only thing I can make is parse the selection string, identify the trees involved and only make a reduced number of friendships. But I was wondering if there is a more efficient way of doing it in ROOT.

Thank you very much

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_ROOT Version:6.24/08
_Platform: Ubuntu 22.04
_Compiler: 11.4.0

2

A priori you just need:

ch0->AddFriend(ch1);
ch0->AddFriend(ch2);
...
ch0->AddFriend(chN);
ch0->Draw( ">>myList" , Selection );
TEventList *acclist = (TEventList*) gDirectory->Get("myList") ;
acclist->SetDirectory(0);

should be enough …

Also, friend of a friend is a friend, so this should also work:

ch0->AddFriend(ch1);
ch1->AddFriend(ch2);
ch2->AddFriend(ch3);
3

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