Hi John,
I do not see any problem with your macro.
You construct a variable bin size histogram and you fill it
with one entry per bin. You see a flat distribution with all values=1.
Concerning your question about weights:
See URL:
http://root.cern.ch/root/html/TTree.html#TTree:Draw
You can read:
selection is an expression with a combination of the columns.
In a selection all the C++ operators are authorized.
The value corresponding to the selection expression is used as a
weight
to fill the histogram.
If the expression includes only boolean operations, the result
is 0 or 1. If the result is 0, the histogram is not filled.
In general, the expression may be of the form:
value*(boolean expression)
if boolean expression is true, the histogram is filled with
a weight = value.
Examples:
selection1 = "x<y && sqrt(z)>3.2"
selection2 = "(x+y)*(sqrt(z)>3.2"
selection1 returns a weigth = 0 or 1
selection2 returns a weight = x+y if sqrt(z)>3.2
returns a weight = 0 otherwise.
Note that in 2.21/08, the selection cannot be just one variable.
ntuple.Draw("x","y") will not produce the distribution of x with the
weigth y.
You have to type:
ntuple.Draw("x',"1*y")
This problem is already fixed in the dev version 2.22.
Rene Brun
John Richardson wrote:
>
> Hi Rene,
> thanks for your prompt response!
>
> Please find an attatched script to illustrate my finding
> (for_rene.C).
> This puts 16 values of 'a' into an ntuple then projects 'a'
> first into a variable binned histo (twalk1) then into an equal
> binned histo (twalk2).
> The bin boundaries for twalk1 are calculated as the mid points
> between the data values.
>
> The root version I am using is 2.21/08 (Solaris).
>
> By the way, a quick question about ntuple plotting...
> If I want to histogram one parameter from an ntuple (a)
> and use another (b) as the weight, how do I do this?
> In paw I used to just put the name of the 'weight
> variable' in the logic string defining the cuts
> e.g. n/proj 200 100.a b.and.c<100
>
> I've tried to do this kind of thing:
>
> ntuple1->Project("twalk2","a","(b)&&(c<100.0)","")
>
> without success.
>
> Thanks,
> John
>
> On Sun, 13 Jun 1999, Rene Brun wrote:
>
> > Hi John,
> > This should work.
> > Can you tell me what is the version of root ?
> > Could you send me a small file with a 5 lines long macro showing the
> > problem?
> >
> > Rene Brun
> >
> >
> > On Sun, 13 Jun 1999, John Richardson wrote:
> >
> > >
> > > Has anyone attempted to project ntuple data into a histogram
> > > with non-equal bin widths?
> > >
> > > I find that using
> > >
> > > ntuple->Draw("a>>histid","","");
> > > or
> > > ntuple->Project("histid","a","","");
> > >
> > > work just fine so long as the TH1F called histid has equal bins.
> > > If histid has been set up with variable binning however, the
> > > bin assignment of the data seems to be corrupt.
> > > Perhaps there is something special I need to do for this
> > > case. Can anyone comment?
> > >
> > > John Richardson.
> > >
> >
> >
>
> ------------------------------------------------------------------------
> {
> gROOT->Reset();
> TNtuple *ntuple1 = new TNtuple("ntuple1","","a:b");
>
> Float_t outer_values[16];
> Float_t bin_edges[17];
>
> Int_t ii;
> Int_t nouter;
>
> outer_values[0] = 2590.0;
> outer_values[1] = 2666.0;
> outer_values[2] = 2781.0;
> outer_values[3] = 2933.0;
> outer_values[4] = 3124.0;
> outer_values[5] = 3352.0;
> outer_values[6] = 3619.0;
> outer_values[7] = 3924.0;
> outer_values[8] = 4267.0;
> outer_values[9] = 4648.0;
> outer_values[10] = 5181.0;
> outer_values[11] = 6324.0;
> outer_values[12] = 7848.0;
> outer_values[13] = 10134.0;
> outer_values[14] = 14706.0;
> outer_values[15] = 24963.0;
>
> /* Calculate the bin boundaries */
> bin_edges[0] = outer_values[0]-(outer_values[1]-outer_values[0])/2.0;
> for (ii=0; ii<16; ii++)
> {
> bin_edges[ii+1] = 2.0*outer_values[ii]-bin_edges[ii];
> }
>
> for (ii=0; ii<16; ii++)
> {
> ntuple1->Fill(outer_values[ii],0.0);
> }
>
> /* Variable bin histo */
> TH1F *twalk1 = new TH1F("twalk1","Timewalk1", 16, bin_edges);
>
> /* Equal bin histo */
> TH1F *twalk2 = new TH1F("twalk2","Timewalk2", 100, 0.0, 30000.0);
>
> ntuple1->Draw("a>>twalk1","","");
> ntuple1->Draw("a>>twalk2","","");
>
> }
This archive was generated by hypermail 2b29 : Tue Jan 04 2000 - 00:43:34 MET