Setting bins for TTree.Draw

From: Pasha Murat (murat@cdfsga.fnal.gov)
Date: Tue May 19 1998 - 22:14:35 MEST 

William Love writes:
 >     I plot a histogram from a TTree (made with h2root) of
 >  an integer variable and ROOT picks bad bins.  I tried to do 
 >  TH1 *hrows = new TH1("hrows","TPC rows",45,0.5, 45.5);
 >     to set good bins and then 
 >  h10.Draw("row>>+hrows");
 >     but I got 
 >  Warning in <TTree::Draw>: Deleting old histogram with different dimensions
 >     and the same wrong-headed histogram.  There seems to be no
 >  TTree.SetBins method.  You used to could do graph/hplot/null in
 >  PAW and then draw on the premade plot.  Must be able to do it
 >  in ROOT?

	Bill:

TTree::Draw acts like nt/plot, so it does binning automatically.

You can book your histogram with TH1* constructor and then use TTree::Project
which projects ntuple contents into a histogram:

	tree->Project("hist","parameter","cuts")

see TTree.h (or ROOT docs) for more detail (also consider asking Valery, 
who is supposed to sit in one of the nearby offices).

						Regards, Pasha.

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