RE: (no subject)

> t->GetBranch("fEvent")->GetEntry(1)
> and it reads zero bytes. Why this is normal?

Because (see previous mail) this is reading the 2nd entry of the branch in the __first__ file/tree. (the branch belong to a TTree not directly to the TChain)

Cheers,
Philippe.

-----Original Message-----
From: owner-roottalk_at_pcroot.cern.ch [mailto:owner-roottalk_at_pcroot.cern.ch] On Behalf Of Dmitry Naumov
Sent: Thursday, November 24, 2005 11:58 AM To: Rene Brun
Cc: roottalk_at_cern.ch
Subject: Re: [ROOT] (no subject)

Rene,
I do not understand your answer. If I have 1 entry in t1 and 1 entry in t2 and doing TChain of t1 and t2 I expect to have in total 2 entries. Is not it?
I read first entry from the TChain with
t->GetBranch("fEvent")->GetEntry(0)
and it reads 425 bytes. Then I try read the second entry from the TChain (first entry
from t2 which is there as I wrote you) with t->GetBranch("fEvent")->GetEntry(1)
and it reads zero bytes. Why this is normal? Dmitry

Rene Brun wrote:

> Dmitry,
>
> When you do
> root [5] t2->GetBranch("fEvent")->GetEntries()
> you get 1 entry. So it is normal that
> root [4] t->GetBranch("fEvent")->GetEntry(0)
> (Int_t)425
> root [5] t->GetBranch("fEvent")->GetEntry(1)
> (Int_t)0
> The last command must return 0, since you only have one entry.
>
> Rene
>
>
> On Thu, 24 Nov 2005, Dmitry Naumov wrote:
>
>> Sorry, I forgot to mention that I first tried what you suggested and
>> it did not work (By the way
>> why it should work if the tree can have in principle different
>> branches each having
>> different number of events? What does it mean "Entries" in this case?)
>> Thus I though that you probably meant setting number of events in the
>> given branch.
>> Just a check of your first message:
>>
>> root [0] TChain *t = new TChain("nuclon")
>> root [1] t->AddFile("t1.root")
>> (Int_t)1
>> root [2] t->AddFile("t2.root")
>> (Int_t)1
>> root [3] t->SetEntries(2)
>> (Long64_t)2
>> root [4] t->GetBranch("fEvent")->GetEntry(0)
>> (Int_t)425
>> root [5] t->GetBranch("fEvent")->GetEntry(1)
>> (Int_t)0
>>
>>
>> Just a check that each event has its 1 event:
>> root [0] TFile f1("t1.root")
>> root [1] TTree *t1 = (TTree*)f1.Get("nuclon")
>> root [2] t1->GetBranch("fEvent")->GetEntries()
>> (const Long64_t)1
>> root [3] TFile f2("t2.root")
>> root [4] TTree *t2 = (TTree*)f2.Get("nuclon")
>> root [5] t2->GetBranch("fEvent")->GetEntries()
>> (const Long64_t)1
>>
>> Rene Brun wrote:
>>
>>> You did not read my mail correctly. I told you to do
>>> t->SetEntries(nentries);
>>> and not
>>> t->GetBranch("fEvent")->SetEntries*();
>>>
>>> Rene Brun
>>>
>>> On Thu, 24 Nov 2005, Dmitry Naumov wrote:
>>>
>>>> Dear Rene,
>>>>
>>>> thank you for this advice. I tried it but it does not read anyway
>>>> the second event:
>>>>
>>>> root [0] TChain *t = new TChain("nuclon")
>>>> root [1] t->AddFile("t1.root")
>>>> (Int_t)1
>>>> root [2] t->AddFile("t2.root")
>>>> (Int_t)1
>>>> root [3] t->GetBranch("fEvent")->SetEntries(2)
>>>> root [4] t->GetBranch("fEvent")->GetEntries() // to check!
>>>> (const Long64_t)2
>>>> root [5] t->GetBranch("fEvent")->GetEntry(0)
>>>> (Int_t)425 // OK
>>>> root [6] t->GetBranch("fEvent")->GetEntry(1)
>>>> (Int_t)0 // empty ?!
>>>>
>>>> root Version 5.02/00 Dmitry
>>>>
>>>> Rene Brun wrote:
>>>>
>>>>> Dmitry,
>>>>>
>>>>> Call t->SetEntries(nentries);
>>>>> where nentries is the number of entries if your branches.
>>>>>
>>>>> Rene Brun
>>>>>
>>>>> On Thu, 24 Nov 2005, Dmitry Naumov wrote:
>>>>>
>>>>>> Dear rooters,
>>>>>>
>>>>>> I have a strange problem:
>>>>>> I create TTree with two branches: fRunPars and fEvent.
>>>>>> fRunPars is filled only once and it containes simulation settings
>>>>>> fEvent s filled for each event:
>>>>>>
>>>>>> fTree->GetBranch("fEvent")->Fill()
>>>>>>
>>>>>> Now I created a set of files with these trees. I want to make a
>>>>>> TChain of them:
>>>>>> TChain *t = new TChain("nuclon");
>>>>>> t->AddFile("t1.root"); // has 1 event
>>>>>> t->AddFile("t2.root"); // has 1 event
>>>>>> t->GetEntries(); // gives 0. It is OK because TTree
>>>>>> // has two branches one of
>>>>>> which is filled
>>>>>> // many times, another
>>>>>> only once, thus Entries probably has no sense
>>>>>> t->GetBranch("fEvent")->GetEntries(); // gives 1 ?! Why not 2?
>>>>>>
>>>>>> If I do
>>>>>> t->GetBranch("fEvent")->GetEntry(0); // it is OK
>>>>>> t->GetBranch("fEvent")->GetEntry(1); // this event is empty.
>>>>>>
>>>>>>
>>>>>> Do I misunderstand something? Many thanks in advance, Dmitry
>>>>>>
>>>>
>>
Received on Thu Nov 24 2005 - 18:42:13 MET