Df 0 0 6_Ranges

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

Author: Danilo Piparo
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Monday, July 06, 2020 at 11:31 AM.

A simple helper function to fill a test tree: this makes the example stand-alone.

In [1]:
%%cpp -d
void fill_tree(const char *treeName, const char *fileName)
{
   ROOT::RDataFrame d(100);
   int i(0);
   d.Define("b1", [&i]() { return i; })
      .Define("b2",
              [&i]() {
                 float j = i * i;
                 ++i;
                 return j;
              })
      .Snapshot(treeName, fileName);
}

We prepare an input tree to run on

In [2]:
auto fileName = "df006_ranges.root";
auto treeName = "myTree";
fill_tree(treeName, fileName);

We read the tree from the file and create a rdataframe.

In [3]:
ROOT::RDataFrame d(treeName, fileName);

Usage of ranges

Now we'll count some entries using ranges

In [4]:
auto c_all = d.Count();

This is how you can express a range of the first 30 entries

In [5]:
auto d_0_30 = d.Range(0, 30);
auto c_0_30 = d_0_30.Count();

This is how you pick all entries from 15 onwards

In [6]:
auto d_15_end = d.Range(15, 0);
auto c_15_end = d_15_end.Count();

We can use a stride too, in this case we pick an event every 3

In [7]:
auto d_15_end_3 = d.Range(15, 0, 3);
auto 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.

In [8]:
auto d_0_50 = d.Range(0, 50);
auto 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.

In [9]:
auto 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!

In [10]:
cout << "Usage of ranges:\n"
     << " - All entries: " << *c_all << endl
     << " - Entries from 0 to 30: " << *c_0_30 << endl
     << " - Entries from 15 onwards: " << *c_15_end << endl
     << " - Entries from 15 onwards in steps of 3: " << *c_15_end_3 << endl
     << " - Entries from 0 to 50, odd only: " << *c_0_50_odd_b1 << endl
     << " - First three entries of all even entries: " << *c_0_3_after_even_b1 << endl;

return 0;
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: 28
 - Entries from 0 to 50, odd only: 25
 - First three entries of all even entries: 3

Draw all canvases

In [11]:
gROOT->GetListOfCanvases()->Draw()