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Reference Guide
df006_ranges.py File Reference



Detailed Description

View in nbviewer Open in SWAN 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(0, 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
d_15_end_3 = d.Range(15, 0, 3)
c_15_end_3 = d_15_end_3.Count()
# The Range is a 1st class citizen in the RDataFrame graph:
# not only actions (like Count) but also filters and new columns can be added to it.
d_0_50 = d.Range(0, 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())
March 2017
Danilo Piparo

Definition in file df006_ranges.py.

Ta Range(0, 0, 1, 1)
ROOT's RDataFrame offers a high level interface for analyses of data stored in TTrees,...
Definition: RDataFrame.hxx:42