Re: Histos from two files

Hello Rene,

Short version: I solved my problem with the original design, obviating the need to read in the histo file and save the same file to a different name.

Long version:
Although your solution occured to me, "B = (TH1*)temp1->Get("A"); " it was my intention to avoid several thousound Get statements. That would require me to run through an entire list of histogram names. I originally tried implementing code that simply opens two files and takes information from set A and holds that file open for the duration of the analysis code, saving histo set B to a new file. As I said I got several thousand errors when I did that. It is as if my pointers to set A became invalid half way through the analysis. It might be that the C++ code was rearranging memory out from underneath me, and I didn't know how to stop it. Alternate designs seemed highly inefficent no matter how I did things, so I retried my original idea (two files open at the same time, writing only set B to disk).

I was using FindObjectAny to read in my histograms from set A, rather than the Get method. A bad habit I suppose, but it let me ignore subdirectories, which made things easier (for me). I just now rewrote the code to go into the correct subdirectory and use Get, and now everything works as I designed it. No more thousands of errors, and my results match what I got before using the database technique.

Thanks again for the help.

• John

Rene Brun wrote:

>
> Could you explain what you intend to do with the statement:
> temp1->Write("temp2.root");
>
> It could be that what you want to do is simply this:
>
> void temp() {
>
> TFile *temp1, *temp2;
> TH1D *A, *B;
>
> temp1=new TFile("temp1.root","recreate");
> A=new TH1D("A","plot1",10,0,10);
> A->Fill(5,1); //etc
> A->Write();
> delete temp1;
> delete A;
>
> temp1=new TFile("temp1.root");
> temp2=new TFile("temp2.root","update");
> B = (TH1*)temp1->Get("A");
> B->Fill(6,2.5); //etc
> B->Write();
> delete temp1;
> delete temp2;
> delete B;
> }
>
> Rene Brun
>
>
> Dr. John Krane wrote:
>
>> Hi everyone,
>>
>> I am working with several thousand histograms at a time. The first
>> set "A" is created from info in a database. The second set "B" is
>> created from info in the first set of histograms. I have a set of
>> code that works by consulting the db, creating set A, then
>> immediately creating set B, and writing one big (big!) histogram file
>> to disk. It takes 10 minutes to run.
>>
>> I want to make histo set A and save it to disk. Then anytime I
>> update my analysis, I read in set A, create set B within a second
>> histo file, and save only B back to disk at that time (leaving the
>> file with set A unchanged on disk). This should be simple, but when
>> I do it I get
>>
>> Error in <TFile::ReadBuffer>: error reading all requested bytes from
>> file output_index_1996.root, got 0 of 18287
>> R__unzip: error in header
>>
>> ...a few thousand times. So I have given up and am trying a new
>> plan. (But if you are really curious about the above problem, email
>> me directly!) My new plan is to read in set A, create histogram set
>> B in that same file, and save the whole mess to a big (big!) histo
>> file with a new name. This too seems like it should be easy, but it
>> keeps failing.
>> Could somebody please tell me what is wrong with the following toy
>> code? I want to see "plot1 exists!" but all I ever see is
>>
>> "Error in <TFile::TFile>: file temp2.root does not exist
>> FAILED".
>>
>> I assure you I have tried several combinations (of the original plan
>> and the new plan) but I am very frustrated. I am using Root version
>> 4.04/02g, which is admittedly old, but I don't think such basic
>> functionality TFile has been changed much has it?
>>
>> - John
>>
>> #include <iostream>
>> #include <TFile.h>
>> #include <TH1D.h>
>>
>> void temp() {
>>
>> TFile *temp1;
>> TH1D *plot1;
>>
>> temp1=new TFile("temp1.root","recreate");
>> plot1=new TH1D("plot1","plot1",10,0,10);
>> temp1->Write();
>> temp1->Close();
>> temp1=0;
>>
>>
>> temp1=new TFile("temp1.root","update");
>> temp1->Write("temp2.root");
>> temp1->Close();
>> temp1=0;
>>
>>
>> temp1=new TFile("temp2.root");
>> plot1=0;
>> if (temp1!=0) plot1=(TH1D*)gDirectory->FindObjectAny("plot1");
>> if (plot1!=0) cerr<<"plot1 exists!"<<endl;
>> else cerr<<"FAILED"<<endl;
>>
>> }
>>
>
>
>

-- 

Dr. John Krane
http://jkrane.home.comcast.net

Stock Options Financier, Physicist, ...and Adventurer