Open a file to read data

[AndreM]

Hello,

I dont have a very deep knowlage of root so I would like to know if its possible to read a given .root file so i can see the data inside in the form of columns. I know i can use TBrowser to see the data but that representation gives me an histogram and i would like to see just the raw data i have written inside a given file so i can understand how to perform my analisis.

Thanks for the attention.

Best regards,
André Miranda

[dastudillo]

How to “see inside” an object depends on what type of object it is (TTree, TGraph, TH1…).
From the terminal (outside ROOT) you can do:

$ rootls -l yourfile.root

to see what’s inside, e.g. (1st col. is the type; name is after the year):

$ rootls -l hsimple.root
TProfile  Apr 12 17:27 2022 hprof;1  "Profile of pz versus px"
TH1F      Apr 12 17:27 2022 hpx;1    "This is the px distribution"
TH2F      Apr 12 17:27 2022 hpxpy;1  "py vs px"
TNtuple   Apr 12 17:27 2022 ntuple;1 "Demo ntuple"

Supposing you have a TTree named “mytree” (like “ntuple” above), you could open the file directly when opening ROOT and then do mytree->Scan() to see all columns and data:

$ root hsimple.root
   ------------------------------------------------------------------
  | Welcome to ROOT 6.26/06                        https://root.cern |
  | (c) 1995-2021, The ROOT Team; conception: R. Brun, F. Rademakers |
  | Built for linuxx8664gcc on Jul 28 2022, 18:08:51                 |
  | From tags/v6-26-06@v6-26-06                                      |
  | With c++ (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0                   |
  | Try '.help', '.demo', '.license', '.credits', '.quit'/'.q'       |
   ------------------------------------------------------------------

root [0]
Attaching file hsimple.root as _file0...
(TFile *) 0x7fffbe06d280
root [1] ntuple->Scan()
************************************************************************
*    Row   *     px.px *     py.py *     pz.pz * random.ra *       i.i *
************************************************************************
*        0 * 0.0194094 * 0.0118254 * 0.0005165 * 0.2826178 *         0 *
*        1 * 0.3271895 * 0.0378782 * 0.1084877 * 0.4849736 *         1 *
*        2 * -0.294611 * -0.010545 * 0.0869072 * 0.5400436 *         2 *
*        3 * -0.774589 * 0.0484584 * 0.6023373 * 0.6586366 *         3 *
*        4 * -1.430795 * 0.5090636 * 2.3063209 * 0.5196720 *         4 *
*        5 * 0.2889872 * -1.864742 * 3.5607798 * 0.3923139 *         5 *

...etc

[AndreM]

The first part was very usefull thanks. I can now see the objects inside my file, but i cant use the second code for reading, I think its because I just have directory files.

[dastudillo]

https://root.cern/doc/master/group__tutorial__io.html

[Wile_E_Coyote]

rootls -h
rootls -l yourfile.root:*

[AndreM]

So can you understand from this information how many columns of data do I have?
I would like to check, if possible the dimension of the data stored on my file, but im having trouble with that.

[Wile_E_Coyote]

rootls -t yourfile.root:* # prints also TTree branches

[AndreM]

Making that in my file comes with an error:

[Wile_E_Coyote]

The first “bold” string in each line is the name of the class of the object that is stored (e.g., “TTime”, “TH1D”, “TH2I”).

Well, the “CalibrationCoefficient” class is not a standard ROOT class. You need to inspect its documentation (or contact its authors).

@Axel / @etejedor Looks like one needs to improve the parser so that it does not die on unknown classes.

[Axel]

Thanks, I have created `rootls` should not show errors when seeing a branch of class without dictionary · Issue #11675 · root-project/root · GitHub