Christoph Ernst wrote: > > Hello, > > Is there a simple way to rescale the y-axis of a TH1 when you plot it from > TTree::Draw()? > For example I want to draw a pt spectrum via tree->Draw("pt"). But as > 1/pt * dN/dpt not just as dN/dpt. > Also, I would like to plot histos from a Tree where each entry has a > specific weight w (something like dw/dx). In a loop I would simply say > h1->Fill(x_i, w_i);. > But I cannot figure out how to do this in the nice way of TTree::Draw(). > If TTree::Draw() can't do it, what do you think is the best alternative? > Hi Christoph, You can do all that in TTree::Draw in the following way: tree->Draw("pt>>hpt","pt*(xxx < yyy && ...)" where (xxx < yyy && ...) is a selection expression involving one or more Tree variables. All events satisfying the selection will get the weight "pt" The resulting histogram will be "hpt". The second parameter of TTree::Draw is the "event-weight" expression. If the result of the expression is null, the event is not histogrammed. In the above example, if (xxx < yyy && ..) is false, the expression is zero, otherwise it is 1. Rene Brun
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