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Hi Bob, Hopefully the following explanation answers your questions. 
 
1) The histogram(name) method in EventAnalyzer returns a histogram. You can
do anything with that histogram that you would do with a histogram created
using new Histogram(name). E.g.
 
        histogram("xyz").fill(10);
        double mean = histogram("xyz").getMean();
        Histogram xyz = histogram("xyz");
 
As you know a convenient feature of the histogram method is that you can
dynamically create the title as part of your analysis, e.g.
 
        PDGID id = particle.getType().getPDGID();
        histogram("Energy-"+id).fill(particle.getEnergy());
        
2)  To extract information from a Histogram you have to first fetch the
partition which is the subcomponent of the histogram that actually keeps
track of the data. Use Histogram.getPartition(). There are many different
types of partition, and if you didnt specify a particular type the histogram
will choose one for you based on which fill method you used. (A corollary is
that you should not call getPartition() until after you have filled the
histogram).  Assuming you used the 1D fill methods, then the partition will
be a subclass of Abstract1DPartition. Abstract1DPartition contains many
methods for accessing information about the histogram (note that it is
package hep.analysis.partition). Some of the information is hidden inside
the getStatistics() method (see attached example).
 
There is another gotcha, teh default Partitions do not do any binning until
you display the histogram. Therefore any attempt to extract information
which depends on the binning will fail unless you first call
Abstract1DPartition.setBinning(). IE
 
       Histogram xyz = histogram("xyz");
       Abstract1DPartition p = (Abstract1DPartition ) xyz.getPartition(); 
       p.setBinning(100,0,1);
       double[] bins = p.getBins();
       for (int i=0; i<bins.length; i++) out.println("bin["+i+"]="+bins[i]);
 
3) Since 2 is rather complicated, Histogram1D exists as a simpler
alternative. It extends Histogram and adds methods for accessing information
without explicitly knowing about the partition, however as you discovered
you must explicitly create the Histogram1D using new Histogram1D("title"),
which is not as convenient as simply using the histogram("title") method,
espcially if you want to dynamically set the histogram title. 
 
4) You can rename histograms with the rename method, but you must catch the
RenameException, since some histograms may not support being renamed. In
this instance you probably don't really want to use renaming.
 
I've attached an example which illustrates all of this.
 
Tony

-----Original Message-----
From: Robert J. Wilson [mailto:[log in to unmask]]
Sent: Friday, November 17, 2000 5:30 PM
To: lcd-sim
Subject: Extracting information from histograms.


  
Does anyone have an example of how to extract histogram information from
histograms created with the EventAnalyzer histogram method. I found the
information on Histogram sub-classes (Histogram1D etc.) that provides the
methods I want, but I cannot get them to work (I won't bore or amuse you
with my numerous attempts).  My analysis code is structured something like
this: 

public class MCGenAnal01 extends AbstractProcessor 
{ 
   LCDEvent _data = null; 


   public void process(LCDEvent event) 
   { 
       final LCDEvent data = (LCDEvent) event; 
       _data = (LCDEvent) event; 
     // Call the first analysis module 
       MCGenAnal(); 


     // ... other stuff 
        ...... 
   } // process 


 void MCGenAnal() 
 { 
     ........ 
    if (something_really_interesting) 
    { 
     // Make lots of histograms 
        histogram("Momentum of "+pname).fill(ptot); 
     // Extract information like mean, and bin-by-bin entries 
        ?????? 
    } 
    ....... 
 } 
} 


Thanks. 
Bob 

-- 

Robert J. Wilson

Professor of Physics

Department of Physics

Colorado State University

Fort Collins, CO 80523

Phone:   (970) 491 5033

Fax:     (970) 491 7947

Email: [log in to unmask]



August 2000 - July 2001:

========================

Institut de Fisica d'Altes Energies

Universitat Autonoma de Barcelona

E-08193 Bellaterra (Barcelona)

SPAIN

Phone: (011 34) 93 581.33.22

Fax:   (011 34) 93 581.19.38

Email: [log in to unmask]

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