Number TTree in a TChain

[Adrian]

What is the best way of getting the number of active TTree in a TChain?

I am adding a list root files to a TChain with the Add() function. Some of these ROOT files do not contain a required TTree, some others do. In the end, the number of TTree is smaller than the number of files. How can I get the number of active TTree in a TChain so I can loop over them?

I tried to use GetTreeOffsetLen() but it does not work. If there is no TTree in the TChain, it returns 100 (???)

Thank you for your help!

[pcanal]

This is not an ‘expected’ use case. TChain assumes there is a TTree each of the input file and even-though it supports that case, it does not keep track of any statistic on whether the file contained the tree or not.

However you can write a smaller script that discover the information.

TChain ch(....);
ch.Add(....);
auto previous = 0;
auto missing = 0;
for(Long64_t e = 0; e < ch.GetEntriesFast(); ++e) {
   if (ch.LoadTree(e) < 0)
     break;
   if (previous != ch.GetTreeNumber()) {
     if ( (ch.GetTreeNumber() - previous) != 1 ) {
        missing +=  (ch.GetTreeNumber() - previous) - 1;
     }
    previous = ch.GetTreeNumber();
  }
}

where the number you are looking for is stored in missing at the end.

[Adrian]

Thank you for the quick help. I think that can work!