Dear rooters,
the new class TTreeIter is developed, tested and proposed for the wide usage.
This is a kind of iterator for TTree or TChain classes.
Functionally it is combination of TTree::Draw() and TTree::MakeClass().
TTreeIter is almost as flexible as TTree::Draw() and allows the same
complexity of request as TTree::MakeClass()
The user interface is very simple and user friendly. It is based on rather
complicated C++ features but all this complexity is hidden from the user.
SPEED is same as optimised MakeClass (only needed branches are read)
In compiled case (ACLIc) it is faster then TTree::Draw
For several histograms (>3) it is faster then TTree::Draw even in CINT case.
TTreeIter is not supposed to replace TTree::Draw() or TTree::MakeClass().
But there is rather wide range of applications where it is more convenient
then these two.
A simple example.
================
TTreeIter iter;
iter.AddFile("path1/event*.root");
iter.AddFile("path2/event*.root");
// init of user variables
const int &ntrk = iter("fTracks");
const Float_t *&pz = iter("fTracks.fPz");
// Now the user variables ntrk and pz are initialised and according branches
// automatically activated. These variables are referenced to internal
// hidden buffers, which will be automatically updated during iteration.
TH1F *hz = new TH1F("Z","Z distribution",50,-5.,+5.);
// Now iterations
while (iter.Next())
{
for (int itr=0;itr<ntrk;itr++)
{
hz->Fill( pz[itr]);
}
}
iter.Reset(); //ready for next loop
-------------------------------------------------------------------------
For those who is interested, all codes and Makefile are:
Those users who have AFS can get it
from /afs/rhic/star/packages/.DEV/StRoot/StarRoot/*
or
http://rhic.rcf.bnl.gov/~perev/StarRoot/
FILEs:
TTreeIter.txt - this message
TTreeIter.h TTreeIter.cxx TTreeIterLinkDef.h
MakeTTreeIter.mk - make file for Linux (easily modification for others)
- gmake -f MakeTTreeIter.mk
th.C - example to measure speed TTreeIter and Draw
mk.C - example to measure speed MakeClass
All comments, critics and proposals are welcome.
Victor
===================================================================
MORE DETAILED
===================================================================
TTreeIter does the same job as TTree::Draw() or MakeClassb but it is different.
==============================================================================
Comparison with TTree::Draw():
-----------------------------
1. TTree::Draw() uses special language. TTreeIter uses standard C++ or CINT.
2. Selection in TTree::Draw() must be in one line. It is very convenient
for simple case. TTreeIter does not have such limitation. Selection and
weight calculation could be as complex as user needs.
3. To fill several histograms, TTree::Draw() must read the file or the chain
of files several times. TTreeIter does it in one pass.
Comparison with MakeClass:
-------------------------
1. TTreeIter internally uses the same technique as MakeClass. Complexity
of selection is the same
2. For each tree MakeClass generates C++ code which user should use.
TTreeIter is the same for all trees. No code is generated
In this sense TTreeIter is more flexible.
3. If format of tree is changed, MakeClass should be regenerated.
TTreeIter is the same. Only additional needed variable could be declared.
4. Usually not all variables of tree are used. To keep MakeClass fast,
user must activate/deactivate according branches by hands.
In TTreeIter, when user defined and initialised variable
(const Float_t &temp = iter("fTemperature");) according branch
activated automatically and only activated branches are read.
Speed tests:
------------
1 histogram 10000 events CINT interpreter case:
----------------------------------------------
TTree::Draw : 23.49 seconds
TTreeIter : 41.11 seconds
MakeClassNonOpt: 162.39 seconds
MakeClassOpt : 41.99 seconds
So, TTreeIter as fast as optimised MakeClass and both are slower
than TTree::Draw
1 histogram 10000 events ACLiC case:
----------------------------------------------
TTree::Draw : 24.09 seconds
TTreeIter : 9.32 seconds
MakeClassNonOpt : 132.18 seconds
MakeClassOpt : 9.40 seconds
Again, TTreeIter as fast as optimised MakeClass and both are much
faster than TTree::Draw. The last is evident, Draw uses interpretor.
3 histograms 10000 events CINT interpreter case:
----------------------------------------------
TTree::Draw : 35.40 seconds
TTreeIter : 46.57 seconds
MakeClassNonOpt : 164.27 seconds
MakeClassOpt : 47.79 seconds
Here, TTreeIter as fast as optimised MakeClass and both are close
to TTree::Draw. It is because Draw uses separate pass for each histogram.
For the big amount of histograms, TTree::Draw will be slower than
TTreeIter and MakeClassOpt
3 histograms 10000 events ACLiC case:
----------------------------------------------
TTree::Draw : 35.77 seconds
TTreeIter : 16.44 seconds
MakeClassNonOpt : 129.08 seconds
MakeClassOpt : 15.92 seconds
Again, TTreeIter as fast as optimised MakeClass and both are much
faster than TTree::Draw.
Any feedback will be very welcome.
Victor
--
Victor M. Perevoztchikov perev@bnl.gov perev@vxcern.cern.ch
Brookhaven National Laboratory MS 510A PO Box 5000 Upton NY 11973-5000
tel office : 631-344-7894; fax 631-344-4206; home 631-345-2690--
This archive was generated by hypermail 2b29 : Tue Jan 01 2002 - 17:51:09 MET