df006_ranges.py File Reference

Namespaces
namespace	df006_ranges

Detailed Description

Use Range to limit the amount of data processed.

This tutorial shows how to express the concept of ranges when working with the RDataFrame.

 
import ROOT
 
def fill_tree(treeName, fileName):
    df = ROOT.RDataFrame(100)
    df.Define("b1", "(int) rdfentry_")\
      .Define("b2", "(float) rdfentry_ * rdfentry_").Snapshot(treeName, fileName)
 
 
# We prepare an input tree to run on
fileName = "df006_ranges_py.root"
treeName = "myTree"
 
fill_tree(treeName, fileName)
 
# We read the tree from the file and create a RDataFrame.
d = ROOT.RDataFrame(treeName, fileName)
 
# ## Usage of ranges
# Now we'll count some entries using ranges
c_all = d.Count()
 
# This is how you can express a range of the first 30 entries
d_0_30 = d.Range(30) 
c_0_30 = d_0_30.Count()
 
# This is how you pick all entries from 15 onwards
d_15_end = d.Range(15, 0)
c_15_end = d_15_end.Count()
 
# We can use a stride too, in this case we pick an event every 3 entries
d_15_end_3 = d.Range(15, 0, 3)
c_15_end_3 = d_15_end_3.Count()
 
# The Range here acts first on the (whole) RDataFrame graph:
# Not only actions (like Count) but also filters and new columns can be added to it.
d_0_50 = d.Range(50)
c_0_50_odd_b1 = d_0_50.Filter("1 == b1 % 2").Count()
 
# An important thing to notice is that the counts of a filter are relative to the
# number of entries a filter "sees". Therefore, if a Range depends on a filter,
# the Range will act on the entries passing the filter only.
c_0_3_after_even_b1 = d.Filter("0 == b1 % 2").Range(0, 3).Count()
 
# Ok, time to wrap up: let's print all counts!
print("Usage of ranges:")
print(" - All entries:", c_all.GetValue())
print(" - Entries from 0 to 30:", c_0_30.GetValue())
print(" - Entries from 15 onwards:", c_15_end.GetValue())
print(" - Entries from 15 onwards in steps of 3:", c_15_end_3.GetValue())
print(" - Entries from 0 to 50, odd only:", c_0_50_odd_b1.GetValue())
print(" - First three entries of all even entries:", c_0_3_after_even_b1.GetValue())

Usage of ranges:
 - All entries: 100
 - Entries from 0 to 30: 30
 - Entries from 15 onwards: 85
 - Entries from 15 onwards in steps of 3: 29
 - Entries from 0 to 50, odd only: 25
 - First three entries of all even entries: 3

Date

March 2017

Author

Danilo Piparo (CERN)

Definition in file df006_ranges.py.