Logo ROOT  
Reference Guide
 
Loading...
Searching...
No Matches
staff.py File Reference

Detailed Description

View in nbviewer Open in SWAN
example of macro to read data from an ascii file and create a root file with a Tree.

NOTE: comparing the results of this macro with those of staff.C, you'll notice that the resultant file is a couple of bytes smaller, because the code below strips all white-spaces, whereas the .C version does not.

import re, array, os
import ROOT
from ROOT import TFile, TTree, gROOT, addressof
## A C/C++ structure is required, to allow memory based access
gROOT.ProcessLine(
"struct staff_t {\
Int_t Category;\
UInt_t Flag;\
Int_t Age;\
Int_t Service;\
Int_t Children;\
Int_t Grade;\
Int_t Step;\
Int_t Hrweek;\
Int_t Cost;\
Char_t Division[4];\
Char_t Nation[3];\
};" );
## Function to read in data from ASCII file and fill the ROOT tree
def staff():
staff = ROOT.staff_t()
# The input file cern.dat is a copy of the CERN staff data base
# from 1988
f = TFile( 'staff.root', 'RECREATE' )
tree = TTree( 'T', 'staff data from ascii file' )
tree.Branch( 'staff', staff, 'Category/I:Flag:Age:Service:Children:Grade:Step:Hrweek:Cost' )
tree.Branch( 'Divisions', addressof( staff, 'Division' ), 'Division/C' )
tree.Branch( 'Nation', addressof( staff, 'Nation' ), 'Nation/C' )
# note that the branches Division and Nation cannot be on the first branch
fname = os.path.join(str(ROOT.gROOT.GetTutorialDir()), 'io', 'tree', 'cernstaff.dat')
for line in open(fname).readlines():
t = list(filter( lambda x: x, re.split( '\s+', line ) ) )
staff.Category = int(t[0]) # assign as integers
staff.Flag = int(t[1])
staff.Age = int(t[2])
staff.Service = int(t[3])
staff.Children = int(t[4])
staff.Grade = int(t[5])
staff.Step = int(t[6])
staff.Hrweek = int(t[7])
staff.Cost = int(t[8])
staff.Division = t[9] # assign as strings
staff.Nation = t[10]
tree.Fill()
tree.Print()
tree.Write()
#### run fill function if invoked on CLI
if __name__ == '__main__':
A ROOT file is an on-disk file, usually with extension .root, that stores objects in a file-system-li...
Definition TFile.h:53
A TTree represents a columnar dataset.
Definition TTree.h:79
Definition staff.py:1
Author
Wim Lavrijsen

Definition in file staff.py.