TTreeFormula::EvalInstance only gets 2 instances?

ROOT
1

Hi,

I am trying to use TTreeFormula::EvalInstance() but found that I only get at most two
instances. I always get 0.0 if I ask for the third instance or higher. The following code
demonstrates this problem. Did I miss something? Thanks. I am using 4.04/02.

[code]{
TTree* _tree= new TTree(“reduced”,“Reduced Tree”);
Int_t _nc;
Float_t *_xx= new Float_t[10];
_tree->Branch(“nc”, &_nc, “nc/I”);
_tree->Branch(“xx”, _xx, “xx[nc]/F”);

TRandom rand;

for ( Int_t j=0; j<5; j++) {
_nc= 5;
for ( Int_t k=0; k<_nc; k++) {
_xx[k] = rand.Rndm();
}
_tree->Fill();
}

_tree->SetScanField(0);
_tree->Scan(“xx”);

TTreeFormula *tf= new TTreeFormula(“tf”,“xx”,_tree);
cout << “Get entry 3” << endl;
_tree->GetEntry(3);
cout << "instance value " << endl;
for ( Int_t k=0; k<5 ; k++ ) {
cout << k << " " << tf->EvalInstance(k) << endl;
}
}[/code]

[code]
root [12] .x ttftest.C

  • Row * Instance * xx *
  •    0 *        0 * 0.1079150 *

  •    0 *        1 * 0.5874750 *

  •    0 *        2 * 0.3189729 *

  •    0 *        3 * 0.1464375 *

  •    0 *        4 * 0.2992230 *

  •    1 *        0 * 0.0407005 *

  •    1 *        1 * 0.1521224 *

  •    1 *        2 * 0.9564707 *

  •    1 *        3 * 0.4798908 *

  •    1 *        4 * 0.5815624 *

  •    2 *        0 * 0.9404398 *

  •    2 *        1 * 0.2410030 *

  •    2 *        2 * 0.8393390 *

  •    2 *        3 * 0.3083940 *

  •    2 *        4 * 0.4706811 *

  •    3 *        0 * 0.4858036 *

  •    3 *        1 * 0.9754050 *

  •    3 *        2 * 0.2558995 *

  •    3 *        3 * 0.7278150 *

  •    3 *        4 * 0.4584717 *

  •    4 *        0 * 0.1907299 *

  •    4 *        1 * 0.5294313 *

  •    4 *        2 * 0.2968764 *

  •    4 *        3 * 0.9638074 *

  •    4 *        4 * 0.2188322 *

Get entry 3
instance value
0 0.485804
1 0.975405
2 0
3 0
4 0[/code]

2

Hi,

You have to call TTreeFormula::GetNdata:

Int_t n = tf->GetNdata(); for ( Int_t k=0; k<n ; k++ ) { cout << k << " " << tf->EvalInstance(k) << endl; }

Cheers,
Philippe.