Automatic axis range for 2D and 3D histograms

Roofit and RooStats
1

Hi,

I am trying to fill a 2D histogram which have unknown range of X-value, but the range of Y-axis is already known. I use the automatic axis range feature, namely set both the upper and lower limit of X-axis to 0, like this

TH2* h2 = new TH2D("h2", "2D hist", 100, 0, 0, 100, 0, 1);

it works fine for the X-axis. However, it also set automatic limits for Y-axis! Having a check of the source of TH2::BufferEmpty(), I found that it does not distinguish which axis should be automatic, and just reset both. I think it could be smarter to have separated treatment for X and Y axis, like this: (part of BufferEmpty(), not yet tested =P~ )

//...
/// finished checkings

#warning just a demo, not yet tested!
if (CanExtendAllAxes() || fXaxis.GetXmax() <= fXaxis.GetXmin()) {
  //find min, max of entries in buffer
  Double_t xmin = fBuffer[2];
  Double_t xmax = xmin;
  for (Int_t i=1;i<nbentries;i++) {
     Double_t x = fBuffer[3*i+2];
     if (x < xmin) xmin = x;
     if (x > xmax) xmax = x;
  }
  if (fXaxis.GetXmax() <= fXaxis.GetXmin()) {
     THLimitsFinder::GetLimitsFinder()->FindGoodLimits(this,xmin,xmax);
  } else {
     fBuffer = 0;
     Int_t keep = fBufferSize; fBufferSize = 0;
     if (xmin <  fXaxis.GetXmin()) ExtendAxis(xmin,&fXaxis);
     if (xmax >= fXaxis.GetXmax()) ExtendAxis(xmax,&fXaxis);
     fBuffer = buffer;
     fBufferSize = keep;
  }
}

if (CanExtendAllAxes() || fYaxis.GetXmax() <= fYaxis.GetXmin()) {
  //find min, max of entries in buffer
  Double_t ymin = fBuffer[3];
  Double_t ymax = ymin;
  for (Int_t i=1;i<nbentries;i++) {
     Double_t y = fBuffer[3*i+3];
     if (y < ymin) ymin = y;
     if (y > ymax) ymax = y;
  }
  if (fYaxis.GetXmax() <= fYaxis.GetXmin()) {
     /// instead of 
     /// THLimitsFinder::GetLimitsFinder()->FindGoodLimits(this,xmin,xmax,ymin,ymax);
     /// fork FindGoodLimits()
     /// or we can modify FindGoodLimits()
     TAxis *yaxis = fYaxis;
     Int_t binsx = fXaxis->GetNbins(),newbinsy;
     Double_t xmin = fXaxis->GetXmin(), xmax = fXaxis->Xmax();

     if (ymin >= ymax) {
        if (yaxis->GetLabels()) {ymin  = 0; ymax  = ymin +yaxis->GetNbins();}
        else                    {ymin -= 1; ymax += 1;}
     }

     THLimitsFinder::OptimizeLimits(yaxis->GetNbins(),
           newbinsy,ymin,ymax,
           yaxis->TestBit(TAxis::kIsInteger));

     h->SetBins(binsx,xmin,xmax, newbinsy,ymin,ymax);
     /// end of insertion
  } else {
     fBuffer = 0;
     Int_t keep = fBufferSize; fBufferSize = 0;
     if (ymin <  fYaxis.GetXmin()) ExtendAxis(ymin,&fYaxis);
     if (ymax >= fYaxis.GetXmax()) ExtendAxis(ymax,&fYaxis);
     fBuffer = buffer;
     fBufferSize = keep;
  }
}

/// then fill the buffer to histogram and empty the buffer
//...

The same problem exists in TH3::BufferEmpty().

2

Hi. We’re checking into your question. Will update here later.

3

Hi,

Your requests make sense. since the automatic binning works for all histogram axis. I will add this as a new feature request for next release

Best Regards

Lorenzo