Re: Making histogram from a ascii data file

The first argument to TH1::Fill is the x abscissa. In your case, simply replace

      ydata->Fill(ydata2[i]);
by

      ydata->Fill(ydata->GetBinCenter(i+1),ydata2[i]);

Rene Brun

Ivan Pulido wrote:
>
>
> On Fri, May 8, 2009 at 1:55 AM, Rene Brun <Rene.Brun_at_cern.ch> wrote:
>
> Did you check that the array ydata2 is correctly filled before
> filling the histogram?
>
>
> Ok I did check this and it's getting filled correctly, just one
> correction from the original code in the line:
>
> while(fscanf(f,"%lf",&ydata2[i]) == 1) i++;
>
> the format specifier should be %f and NOT %lf, after this the array
> ydata2 gets filled correctly. But apparently the histogram ydata is
> not, Im not getting anything on the canvas.
>
>
>
> Did you check that the values are in the range [0.64,1.63]?
>
>
> Well I have a doubt here, in the line:
> TH1F* ydata = new TH1F("ydata","times measured; Energy
> (q^2)",100,0.64,1.63);
>
> 0.64 and 1.63 are suppoused to be the limits for the x axis, right? so
> if this is the case then it's right.
> On the other hand my ydata (y axis) values are different, they go
> approx from 4.5 to 10000. Im not sure if the parameters/values needed
> for the TH1F are the x limits or y limits. Please clarify this to me.
> Thanks for the response and attention.
>
> NOTE: If it helps I'm attaching two text files with the data so that
> you can see how is my data formatted. The file Im using in the code
> above ("tau_ydata.dat") is there and is the one with a single column
> having the y axis values. The other file attached ("tau2.dat") is the
> one having x values in the first column and y values on the second
> column, just so that you see which are my limits.
>
>
>
>
> Rene Brun
>
>
> Ivan Pulido wrote:
>
> Hi, Im trying to make a histogram from a plain text data file.
> I tried following instructions from
> http://root.cern.ch/drupal/content/binned-data
>
> The histrogram I want to make is in 1D, I try to make an array
> from a plain text data file before filling the histogram as
> suggested in the site. Here are the steps/instructions Im
> following to make this happen, please let me know what is
> wrong. The result is just the canvas with no data in it, just
> the axis, axis tittles and no data.
>
> TH1F* ydata = new TH1F("ydata","times measured; Energy
> (q^2)",100,0.64,1.63);
> float ydata2[100];
> FILE * f = fopen ("tau_ydata.dat","r");
> int i=0;
> while(fscanf(f,"%lf",&ydata2[i]) == 1) i++;
> for (i=0; i<100; ++i) ydata->Fill(ydata2[i]);
> ydata->Draw();
>
> I must tell that the tau_ydata.dat file is read correctly and
> the array ydata2 has the correct values, so I think the
> problem is filling the histogram, since when I draw it Im
> getting nothing. Please help me on this, Im new with ROOT so
> maybe you can point where to find the solution to this or
> anything, maybe this is not the correct way to do it. Thanks
> for the attention.
>
>
>
>
>
> --
> Ivan Pulido
> Estudiante de Física
> Universidad Industrial de Santander
Received on Fri May 08 2009 - 10:27:02 CEST