Hi Nigel,
The TTreeFormula class is used internally by the Root Tree classes.
Normally a user does not see this class at all. You simply specify
your cuts in the selection expression. This expression can be a TCut or
combinations of TCuts.
If you want to use TTreeFormula, I suggest you look at TTree::Scan for
examples of use.
Rene Brun
nigel@kiwi.chm.bnl.gov wrote:
>
> Dear RootTalk,
> I have a ntuple, called ntuple,with columns "run:noise"
>
> I make a TTreeFormula via
>
> TTreeFormula *h=new TTreeFormula("h","run<1000",ntuple)
>
> then when I go
>
> ntuple->Draw("run","h")
>
> I get
> *ERROR 26 :
> Unknown name : "h"
>
> when I try
>
> ntuple->Draw("run","h")
> I get
> Error: Can't call TNtuple::Draw() in current scope
> FILE:/tmp/fileH9aDTt_cint LINE:1
>
> Clearly I am missing the point about TTreeFormula.
> Although this simple example could have been performed
> with a TCut, or even string, I would like to know
> how to use TTreeFormula in general, so when I have a complicated
> formula I can apply it to the ntuple as a cut.
>
> I tried to find an example, but could not. Could someone
> help me out.
>
> Thanks
> Nigel
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