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.

Author: Wim Lavrijsen
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Monday, December 06, 2021 at 09:23 AM.

In [ ]:
import re, array, os
import ROOT
from ROOT import TFile, TTree, gROOT, addressof

A C/C++ structure is required, to allow memory based access

In [ ]:
"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

In [ ]:
staff = ROOT.staff_t()

The input file cern.dat is a copy of the CERN staff data base from 1988

In [ ]:
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

In [ ]:
fname = os.path.join(str(ROOT.gROOT.GetTutorialDir()), '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]