Trouble with accessing the output of Merged TChain

ChangAPI · April 25, 2017, 9:47am

Hi all,

I was able to merge root files together with TChain using the Merge() function, but I could not access the merged tree. I can access the merged tree with TBrowser, but if I try to use a different TTree to access the new root file, I get a nullpointer.
The commands I used is shown below.

TChain* chain=new TChain(“nominal;1”)
chain->Add(“1.root”)
chain->Add(“2.root”)
chain->Merge(“Merged_test.root”)

TFile* f=new TFile(“Merged_test.root”)
TTree* t=(TTree*)f->Get(“nominal;1;1”)

The command then returns:

(TTree *) nullptr

I also tried using:

TTree* t=(TTree*)f->Get(“nominal;1”)
TTree* t=(TTree*)f->Get(“nominal”)

And it still gives me a nullpointer.

What should be done for me to access the merged tree with TTree?

Regards,
Paulo

couet · April 25, 2017, 10:07am

I guess @pcanal can help you.

pcanal · April 25, 2017, 2:22pm

TChain* chain=new TChain("nominal;1")

you meant

TChain* chain=new TChain("nominal")

what does

TFile* f=new TFile("Merged_test.root")
f->ls();

prints?

ChangAPI · April 25, 2017, 2:40pm

Hi @pcanal,

Doing the commands gave me:

TFile** Signal_Merged.root chain files
TFile* Signal_Merged.root chain files
KEY: TTree nominal;1;1 nominal

It’s just the same file with a different name.

pcanal · April 25, 2017, 5:04pm

I see. The addition ;1 is likely to confuse the tool. You could still work with this file but it would be harder. I recommend you recreate it using

TChain* chain=new TChain("nominal")

Cheers,
Philippe.

ChangAPI · April 25, 2017, 8:50pm

Hi @pcanal,
Thank you for your response.

Using “nominal” alone gives me a segmentation violation error.
I need to use “nominal;1” for the TChain to merge.

Regards,
Paulo

pcanal · April 25, 2017, 9:13pm

Where do you use it? Where does it segfault?

ChangAPI · April 26, 2017, 3:22am

Hi @pcanal,

TChain* chain=new TChain(“nominal”)
chain->Add(“1.root”)
chain->Add(“2.root”)
chain->Merge(“Merged_test.root”)

The segfault happens after the Merge function.

pcanal · April 26, 2017, 6:20pm

What is the stack trace? What is the content (output of ls()) for 1.root?

ChangAPI · April 26, 2017, 6:51pm

Hi @pcanal,

The output of the command ls() for 1.root is:

TFile** 1.root
TFile* 1.root
KEY: TTree nominal;1 nominal
KEY: TH1D cut_flow;1 number of events no weight
KEY: TH1D cross_section;1 cross_Section

Same goes with 2.root just replace 1.root with 2.root

pcanal · April 26, 2017, 7:02pm

that looks as expected. When you process crashes, what is the stack trace?

ChangAPI · April 26, 2017, 7:06pm

Here’s the output after the Merge() function when using “nominal”.

*** Break *** segmentation violation
Generating stack trace…
0x0000000119863c6c in TChain::Merge(TFile*, int, char const*) (in libTree.so) + 668
0x0000000116f50049 in
0x00000001084093ad in cling::Interpreter::RunFunction(clang::FunctionDecl const*, cling::Value*) (in libCling.so) + 317
0x0000000108408839 in cling::Interpreter::EvaluateInternal(std::__1::basic_string<char, std::__1::char_traits, std::__1::allocator > const&, cling::CompilationOptions, cling::Value*, cling::Transaction**) (in l
0x0000000108408204 in cling::Interpreter::process(std::__1::basic_string<char, std::__1::char_traits, std::__1::allocator > const&, cling::Value*, cling::Transaction**) (in libCling.so) + 100
0x000000010844387f in cling::MetaProcessor::process(char const*, cling::Interpreter::CompilationResult&, cling::Value*) (in libCling.so) + 415
0x000000010831d56a in TCling::ProcessLine(char const*, TInterpreter::EErrorCode*) (in libCling.so) + 3690
0x0000000107ebc293 in TRint::ProcessLineNr(char const*, char const*, int*) (in libRint.so) + 211
0x0000000107ebcddf in TRint::HandleTermInput() (in libRint.so) + 671
0x000000010806f028 in TUnixSystem::CheckDescriptors() (in libCore.so) + 328
0x000000010806be4d in TMacOSXSystem::DispatchOneEvent(bool) (in libCore.so) + 429
0x0000000107fba2da in TSystem::InnerLoop() (in libCore.so) + 26
0x0000000107fba12b in TSystem::Run() (in libCore.so) + 203
0x0000000107f5eaf4 in TApplication::Run(bool) (in libCore.so) + 36
0x0000000107ebc14c in TRint::Run(bool) (in libRint.so) + 1372
0x0000000107eafe8f in main (in root.exe) + 79
0x00007fff974ba5c9 in start (in libdyld.dylib) + 1

pcanal · April 26, 2017, 7:07pm

this is odd. Can you send me the two files so that I can try to reproduce this?

ChangAPI · April 26, 2017, 7:24pm

These are the test files that I’m currently using:

1.root (174.5 KB)
2.root (936.0 KB)

pcanal · April 26, 2017, 8:04pm

it works fine for me.

Which version of ROOT are you using?

Can you try with a version of ROOT build in debug mode?

ChangAPI · April 27, 2017, 12:56pm

Hi @pcanal,

It turns out that my script was using a different 1.root that has two nominal trees.

TFile** 1.root
TFile* 1.root
KEY: TTree nominal;2 nominal
KEY: TTree nominal;1 nominal
KEY: TH1D cut_flow;1 number of events no weight
KEY: TH1D cross_section;1 cross_Section
KEY: TTree tree;1 tree

Changing the directories on my script slipped my mind, I intended to use the ones that I sent to you.
Anyway, it’s now working as I expect it to be.

Thank you very much for your time.

Regards,
Paulo

pcanal · April 27, 2017, 1:58pm

Even with that file it should have worked (without ever mentioning the cycle ;1) and you really did not want to use the first cycle (;1) which is the older copy of the TTree meta-data.

Cheers,
Philippe.

system · May 11, 2017, 1:59pm

This topic was automatically closed 14 days after the last reply. New replies are no longer allowed.