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---+How to Access Data via Cafe

_by Pedro Mercadante - Last update on 15-Dec-2005_

*How To Make a Processor and Access the Data via Cafe*

On d0server copy the following files to your work directory:

==/home/mercadan/Analises/cafe/zpeak/AddProcessor.sh==

==/home/mercadan/Analises/cafe/zpeak/TClass.cpp==

==/home/mercadan/Analises/cafe/zpeak/TClass.hpp==

==/home/mercadan/Analises/cafe/zpeak/TClass_linkdef.h==

==/home/mercadan/Analises/cafe/zpeak/TClass_t.cpp==

Execute:

==./AddProcessor.sh inv_mass !InvMass==

The first argument is the package name and the second is the processor name. The !AddProcessor.sh creates all the necessary .cpp, .hpp and linkdef.h. We should edit the inv_mass/src/InvMass.cpp. Basically in !InvMass::begin() we initialize the histograms; in !InvMass::processEvent(cafe::Event& event) we process events, do whatever we need and fill the histograms; and in !InvMass::finish() we write the histograms.

To access the data we should look at 
<a href="http://www-d0.fnal.gov/Run2Physics/working_group/data_format/caf/">
http://www-d0.fnal.gov/Run2Physics/working_group/data_format/caf/</a> %BR%
under the class list. 
We can click on   cafe::Event  and see all the objects. 
For exemple getEMscone is a Collection <TMBEMCluster>. 
To access it we need to define a object that is a collection and access the collection via a pointer:

==Collection<TMBEMCluster> fro(event.getEMscone());==

==for(Collection<TMBEMCluster>::const_iterator it = fro.begin() ;==

==it != fro.end(); ++it)==

Now we can access all objects defined in the class TMBEMCluster. For example, Px, Py, Pz:

==float ele_pt = it->Pt() ;==

==float ele_px = it->Px() ;==

==float ele_py = it->Py() ;==

==float ele_pz = it->Pz() ;==

==float ele_E = it->E() ;==

One note for the histograms: we define the histograms in the !InvMass::begin() function and fill in the bool !InvMass::processEvent(cafe::Event& event) function. So don't forget to declare the global variables in the .hpp file.
Topic revision: r2 - 2006-09-18 - SergioLietti
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