Laurent Aphecetche wrote:
> Hi, Rooters,
>
> What's the best way to rebin an histogram (either 1d or 2d ) ?
This is a macro to do the job.
Rene Brun
//======================macro Rebin.C==============================
TH1F *Rebin(TH1F *hold, const Int_t ngroup)
{
// example of ROOT macro to rebin a 1-D histogram hold
// Method:
// a new temporary histogram hnew is created and return to the caller
// The parameter ngroup indicates how many bins of hold have to me
merged
// into one bin of hnew
// Errors are not taken into account
//
// Usage:
// Root > .L rebin.C; //load this macro
// Root > TH1F *hnew = Rebin(hold,2); //to rebin hold grouping 2 bins
in one
//
// This macro will become a new TH1 function (taking care of errors)
// TH1 *TH1::Rebin(const Int_t ngroup)
TAxis *xold = hold->GetXaxis();
Int_t nbins = xold->GetNbins();
Float_t xmin = xold->GetXmin();
Float_t xmax = xold->GetXmax();
if ((ngroup <= 0) || (ngroup > nbins)) {
printf("ERROR in Rebin. Illegal value of ngroup=%d\n",ngroup);
return 0;
}
Int_t newbins = nbins/ngroup;
// create a clone of the old histogram
TH1F *hnew = hold->Clone();
// change name and axis specs
hnew->SetName("hnew");
TAxis *xnew = hnew->GetXaxis();
xnew->Set(newbins,xmin,xmax);
hnew->Set(newbins+2);
// copy merged bin contents (ignore under/overflows)
Int_t bin, i;
Int_t oldbin = 1;
Stat_t bincont;
for (bin = 1;bin<=newbins;bin++) {
bincont = 0;
for (i=0;i<ngroup;i++) {
bincont += hold->GetBinContent(oldbin+i);
}
hnew->SetBinContent(bin,bincont);
oldbin += ngroup;
}
return hnew;
}
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