> Hi,
>
> I have 2 TH2F histograms with different specifications (e.g. y axis is
> the same, but for
> x axis, one goes from -1 to 0 and the other from 0 to 1). How can I
> merge these 2 histograms ?
The macro below can do the job. Modify it at your convenience.
Rene Brun
//--------------------macro merge.C-------------------
{
// example of macro to merge two TH2F with different bin specs
gROOT->Reset();
TH2F *h1 = new TH2F("h1","h1",20,-1,0,40,-1,1);
TH2F *h2 = new TH2F("h2","h2",20,0, 1,40,-1,1);
//fill these histograms with gaussian distributed numbers
Int_t i;
Float_t x,y;
for (Int_t i=0;i<10000;i++) {
y = gRandom->Gaus(0,0.4);
h1->Fill(gRandom->Gaus(-0.5,0.1),y);
h2->Fill(gRandom->Gaus(0.5,0.1),y);
}
// Merge these two histograms into one
// the following algorithm assumes that binning of h1 and h2 can
overlap
TAxis *ax1 = h1->GetXaxis();
TAxis *ay1 = h1->GetYaxis();
TAxis *ax2 = h2->GetXaxis();
TAxis *ay2 = h2->GetYaxis();
Int_t nx1 = ax1->GetNbins();
Int_t nx2 = ax2->GetNbins();
Int_t ny1 = ay1->GetNbins();
Int_t ny2 = ay2->GetNbins();
Int_t nx = nx1 + nx2;
Int_t ny = ny1 + ny2;
Float_t xmin1 = ax1->GetXmin();
Float_t ymin1 = ay1->GetXmin();
Float_t xmax1 = ax1->GetXmax();
Float_t ymax1 = ay1->GetXmax();
Float_t xmin2 = ax2->GetXmin();
Float_t ymin2 = ay2->GetXmin();
Float_t xmax2 = ax2->GetXmax();
Float_t ymax2 = ay2->GetXmax();
Float_t xmin = TMath::Min(xmin1,xmin2);
Float_t ymin = TMath::Min(ymin1,ymin2);
Float_t xmax = TMath::Max(xmax1,xmax2);
Float_t ymax = TMath::Max(ymax1,ymax2);
TH2F *hnew = new TH2F("hnew","h1+h2",nx,xmin,xmax,ny,ymin,ymax);
Int_t binx, biny;
Float_t x,y;
for (binx=1;binx<=nx1;binx++) {
x = ax1->GetBinCenter(binx);
for (biny=1;biny<=ny1;biny++) {
y = ay1->GetBinCenter(biny);
hnew->Fill(x,y,h1->GetCellContent(binx,biny));
}
}
for (binx=1;binx<=nx2;binx++) {
x = ax2->GetBinCenter(binx);
for (biny=1;biny<=ny2;biny++) {
y = ay2->GetBinCenter(biny);
hnew->Fill(x,y,h2->GetCellContent(binx,biny));
}
}
hnew->Draw();
}