Hello!
I want to read out the raw data from a root file (actually a lot of them) and manipulate the data before I do any plots, histograms, etc…
Probably some basic stuff, but somehow for the last few days ROOT always came up with a way of not giving me what I want^^.
Some Background (maybe thats useful):
For my master’s thesis, I wrote a Geant4 application that stores it’s output as NTuples in Root - Files. The code in the application is fairly simple and looks like this:
//#########Snippet#########
//ntuple for GlassPlate data (ID = 1)
//#########################
analysisManager ->
CreateNtuple("GlassPlate_Run" + to_string (runID),"GlassPlateData");
analysisManager -> CreateNtupleSColumn("Particle");
analysisManager -> CreateNtupleIColumn("TrackID");
analysisManager -> CreateNtupleDColumn("TimeStamp");
analysisManager -> CreateNtupleIColumn("GlassPlateID");
analysisManager -> CreateNtupleDColumn("PositionX");
analysisManager -> CreateNtupleDColumn("PositionY");
analysisManager -> CreateNtupleDColumn("PositionZ");
analysisManager -> CreateNtupleDColumn("MomentumDirX");
analysisManager -> CreateNtupleDColumn("MomentumDirY");
analysisManager -> CreateNtupleDColumn("MomentumDirZ");
analysisManager -> CreateNtupleDColumn("Energy");
analysisManager -> FinishNtuple();
//output of time sorted glass plate hits
n_hit = GPHC -> entries();
vector<G4double> USGPHC;
for(G4int i = 0; i < n_hit; i++)
{
USGPHC.push_back( ((* GPHC)[i])->GetTime() );
}
vector<G4double> TSGPHC = USGPHC;
sort(TSGPHC.begin(),TSGPHC.end());
G4SDManager * sdManager = G4SDManager :: GetSDMpointer();
MyGlassPlateSD * GlassPlateSD = (MyGlassPlateSD *)
sdManager -> FindSensitiveDetector("mySim/Detectors/GlassPlate");
vector<G4int> gotLoA = GlassPlateSD -> GetGotLostOrAbsorbed();
for(G4int i = 0; i < n_hit; i++)
{
G4double timestamp = TSGPHC[i];
vector<G4double>::iterator it = find(USGPHC.begin(),
USGPHC.end(),
timestamp);
G4int index = distance(USGPHC.begin(), it);
MyGlassPlateHit * hit = (* GPHC)[index];
if(find(gotLoA.begin(),
gotLoA.end(),
(hit -> GetTrackID()))
== gotLoA.end()
)
{
analysisManager ->
FillNtupleSColumn(1,
0,
hit -> GetPartName());
analysisManager ->
FillNtupleIColumn(1,
1,
hit -> GetTrackID());
analysisManager ->
FillNtupleDColumn(1,
2,
hit -> GetTime() / ps);
analysisManager ->
FillNtupleIColumn(1,
3,
hit -> GetID());
analysisManager ->
FillNtupleDColumn(1,
4,
(hit -> GetEntryPoint()).x() / cm);
analysisManager ->
FillNtupleDColumn(1,
5,
(hit -> GetEntryPoint()).y() / cm);
analysisManager ->
FillNtupleDColumn(1,
6,
(hit -> GetEntryPoint()).z() / cm);
analysisManager ->
FillNtupleDColumn(1,
7,
(hit -> GetMomentumDir()).x() / cm);
analysisManager ->
FillNtupleDColumn(1,
8,
(hit -> GetMomentumDir()).y() / cm);
analysisManager ->
FillNtupleDColumn(1,
9,
(hit -> GetMomentumDir()).z() / cm);
analysisManager ->
FillNtupleDColumn(1,
10,
hit -> GetEtot() / eV);
analysisManager -> AddNtupleRow(1);
}
}Don’t bother with the details of the above snippet if you don’t know Geant4, I just wanted to show, how I filled my NTuples. The snippet shows how I fill one of three NTuples that will be stored in a root file.
Basically, if I tell my App to do a 1000 runs, I get 1000 root files where each one contains 3 NTuples with the data.
Optionally, I could also only produce one root file as output which will then contain 3000 NTuples with the data. But the problem remains: I need a fast way of reading the values stored in all these NTuples and store them in a way, that makes it easy to manipulate them.
Now to ROOT:
ROOT recognizes my ntuples as TTree Objects which have a TBranch object for every column of the NTuple.
I wrote a little code that gives me access to the Files and Trees, and the Print() method shows, that the data is there:
//############Code Snippet############
//(myFile is the TFile object to a corresponding .root-File, myTree is a TTree object to one of the trees in the file)
//####################################
myFile -> ls();
for(int i = 0; i < myTree -> GetNbranches(); i++)
{
TBranch * theBranch =
(TBranch *) (myTree -> GetListOfBranches()) -> At(i);
theBranch -> Print();
}
//############OUTPUT:############
/home/fdachs/Dropbox/Geant4/Projects/mySimulation/build/Output/root/rootData_31-3-2016_Run3.root
TFile** /home/fdachs/Dropbox/Geant4/Projects/mySimulation/build/Output/root/rootData_31-3-2016_Run3.root
TFile* /home/fdachs/Dropbox/Geant4/Projects/mySimulation/build/Output/root/rootData_31-3-2016_Run3.root
KEY: TTree Scintillator_Run3;1 PrimaryData
KEY: TTree GlassPlate_Run3;1 GlassPlateData
KEY: TTree SPADs_Run3;1 SPADData
*Br 0 :Particle : Char_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 215245 bytes File Size = 18515 *
*Baskets : 5 : Basket Size= 32000 bytes Compression= 11.13 *
*............................................................................*
*Br 1 :TrackID : Int_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 95919 bytes File Size = 28936 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 2.21 *
*............................................................................*
*Br 2 :TimeStamp : Double_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 143614 bytes File Size = 68796 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.40 *
*............................................................................*
*Br 3 :GlassPlateID : Int_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 95949 bytes File Size = 17330 *
*Baskets : 1 : Basket Size= 32000 bytes Compression= 3.70 *
*............................................................................*
*Br 4 :PositionX : Double_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 143614 bytes File Size = 53642 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.79 *
*............................................................................*
*Br 5 :PositionY : Double_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 143614 bytes File Size = 55196 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.74 *
*............................................................................*
*Br 6 :PositionZ : Double_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 143614 bytes File Size = 61880 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.55 *
*............................................................................*
*Br 7 :MomentumDirX : Double_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 143635 bytes File Size = 71916 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.34 *
*............................................................................*
*Br 8 :MomentumDirY : Double_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 143635 bytes File Size = 71879 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.34 *
*............................................................................*
*Br 9 :MomentumDirZ : Double_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 143635 bytes File Size = 71876 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.34 *
*............................................................................*
*Br 10 :Energy : Double_t GlassPlate_Run3 *
*Entries : 11896 : Total Size= 143593 bytes File Size = 70479 *
*Baskets : 2 : Basket Size= 32000 bytes Compression= 1.36 *
*............................................................................*
So there are 11 Branches with the names that I gave them in my Geant4 app and they contain, for this particular run, 11896 entries and the branches seem to know what format they’re storing.
A look at the files with TBrowser even shows me Histograms of the data, so the root files should be OK.
Finally my Question:
Is there a way of getting the actual values of the entries of the Branches and putting them, for example, into an array or vector?
Basically like:
vector<double> energies;
for(int i = 0; i < theBranch -> GetEntries(); i++)
{
energies.push_back(theBranch -> GetEntry(i));
}Sadly, the GetEntry() method only returns the number of bytes read, but not the value of the entry (why is this not called GetBytesRead() or something??) but I think you know what I mean.
I feel like I missed something obvious and the answer is easy, but I can’t see it for some reason. Maybe ROOT is just meant to be used in a different way but all the tutorials I could find either only explain about the ROOT shell or super easy examles that aren’t much use 
If you could help me out or point me towards a similar post in the forum, I would be most grateful!!
I looked through many posts myself, but didn’t find anything that could help me 
best regards,
Badger
