doc/v616/df006__ranges_8py.html

import ROOT


def fill_tree(treeName, fileName):

    tdf = ROOT.ROOT.RDataFrame(100)

    tdf.Define("b1", "(int) tdfentry_")\

       .Define("b2", "(float) tdfentry_ * tdfentry_").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.

RDF = ROOT.ROOT.RDataFrame

d = RDF(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())

Range
Ta Range(0, 0, 1, 1)