List of all histograms in a file

ROOT
1

I want to write code following this scheme:

1. open root file 2. get list of all histograms in this file 3. loop over list 3a. draw histogram list[i]

However, I don’t know how to perform step 2. Is there any way to do that?
The file containes histograms only.

Thanks a lot!
Cheers,
Martin

1 Like
2

see in $ROOTSYS/tutorials/io/loopdir.C

Jan

3

First comment: In my installation I found loopdir.C at $ROOTSYS/tutorials/loopdir.C
I am using 5.13/02.

Second comment: I have a root file with a subdirectory which has many histograms which can be seen in TBrowser. I find that when I use the keys method I only get the key for the subdirectory. The keys to the histograms are never returned. It would seem that I need to set my directory to the subdirectory and then fetch the keys. I tried this with this code:

TFile *f = new TFile(“T0Classic_classic_t0_fitter.root”);
f->cd(“classic_t0_fitter”);
TIter next(f->GetListOfKeys());
TKey key;
nhist=0;
while ((key = (TKey)next())) {
nhist++;
cout << "Key " << nhist << endl;
cout << " Classname " <GetClassName() << endl;
cout << " Title " <GetTitle() << endl;
}

This produces this output:

Key 1
Classname TDirectory
Title classic_t0_fitter

However, there are 100’s of histrograms in the “classic_t0_fitter” subdirectory which I am not getting the keys for. What do I need to do differently to get them?

Thanks much

4

Hi diehl,

  1. $ROOTSYS/tutorials/io/loopdir.C for ROOT >= 5.14.00
  2. see this link root.cern.ch/phpBB2/viewtopic.php?t=1659

Jan

5

Thanks Jan for the quick reply. I also found a local root expert who helped me solve my problem. The problem was this line of my code:

f->cd(“subdirectory”)
TIter next(f->GetListOfKeys());

I thought that the GetListofKeys() would retrieve the keys of the subdirectory. However, I only get the list of keys in the highest directory level of the file, which in my case is just one subdirectory.

What one needs to do is this:

f->cd(“subdirectory”)
TIter next(gDirectory->GetListOfKeys());

gDirectory points at the current directory which I’ve cd’ed to.

Thanks for the help, Edward Diehl

6

See root.cern.ch/root/htmldoc/TFileIter.html also

[code]{
TFile *f = new TFile(“test.root”);
TFileIter readObj(f);
// the number of the object available directly from “MyDataSet.root"
Int_t size = readObj.TotalKeys();
printf(” The total number of the objects: %d\n",size);

//------------------------------------------------------
// Loop over all objects, read them in to memory one by one

printf(" – > Loop over all objects < – \n");
// Attention: ROOTForum corrupted the following C++ “for” statement !!!
// See the link above for the correct text !!!
for( readObj = 0; int(readObj) GetName()
,nextObject->IsA()->GetName()
,(const char *)readObj
);
delete nextObject;
}[/code]

7

Valeri,

Two remarks
-That is not what the user wants. He needs to navigate in sub-directories too.
-when posting code as you do, check the button “Disable html in post”

Rene

8

[quote=“brun”]Two remarks
-That is not what the user wants. He needs to navigate in sub-directories too.[/quote]OO :bulb: Yes :bulb: I have to fix this immidiately :exclamation: . My solution was narrowed by local :blush: needs

[quote=“brun”]-when posting code as you do, check the button “Disable html in post”[/quote]Thank you Rene, May be this should be default. I believe (I do know) many people have had the same problem and none thought it can be fixed and even worth to complain.

9

Valeri,

To set the “disable html” option pernanently on, click on the “Profile” button
at the top of the page.

Fons changed the default for all new users to disable html.

Rene