[ROOT] non-constant 2-dimensional arrays?

From: cstrato@EUnet.at
Date: Fri Dec 29 2000 - 19:57:44 MET 

Dear Rooters

I would like to read tables containing (x, y, value) in each line,
as an array ar[][]. However, the number of rows and columns would
always be different.

In an example given by Rene Brun in the mail from Sun Feb 13 2000
(http://root.cern.ch/root/roottalk/roottalk00/0367.html)
he has written “I assume that your array has a constant size in x and y”

and has presented the file “array.C”

Is there an easy way to generalize this example, when the dimensions
are not constant?

As a first attempt I have modified the file “array.C” in a way that
it uses class TMatrix instead of a 2-dim array (see below).

Since I do not need matrix calculations, but only a 2-dim array,
especially
arrays with the size of about 1000 x 1000, my question is, is the use
of class TMatrix the right way or does there exist a better solution?

Thank you in advance
Christian Stratowa
Vienna, Austria


//----------file array.C
#include "TMatrix.h"
#include <iostream.h>
#include <math.h>

void fillarray(Int_t nrow,Int_t ncol)
{
   TFile f("test.root","recreate");
   TTree T("T","a simple test with an array");
   TMatrix *ma = new TMatrix(nrow,ncol);
   T.Branch("ma",&ma,64000,0);
   for (Int_t i=0;i<nrow;i++) {
      for (Int_t j=0;j<ncol;j++) {
         ma(i,j) = gRandom->Gaus(i,j);
      }
   }
   T.Fill();
   T.Write();
}

void readarray()
{
   Int_t nrow;
   Int_t ncol;
   TMatrix *ma;

   TFile *f = new TFile("test.root");
   TTree *T = (TTree*)f->Get("T");
   T->SetBranchAddress("ma",&ma);
   TH1F *hed = new TH1F("hed","ma values",100,-100,100);
   T->GetEntry();
   nrow = ma->GetNrows();
   ncol = ma->GetNcols();
   for (Int_t i=0;i<nrow;i++) {
      for (Int_t j=0;j<ncol;j++) {
         hed->Fill(ma(i,j));
      }
   }
   printf("nrows = %i, ncols = %i \n",nrow,ncol);
   hed->Draw();
}

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