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Reference Guide
df006_ranges.C 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.

// A simple helper function to fill a test tree: this makes the example
// stand-alone.
void fill_tree(const char *treeName, const char *fileName)
{
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
auto fileName = "df006_ranges.root";
auto treeName = "myTree";
fill_tree(treeName, fileName);
// We read the tree from the file and create a RDataFrame.
ROOT::RDataFrame d(treeName, fileName);
// ## Usage of ranges
// Now we'll count some entries using ranges
auto c_all = d.Count();
// This is how you can express a range of the first 30 entries
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
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
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.
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.
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!
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
(int) 0
Date
March 2017
Author
Danilo Piparo

Definition in file df006_ranges.C.

df006_ranges
Definition: df006_ranges.py:1
ROOT::RDataFrame
ROOT's RDataFrame offers a high level interface for analyses of data stored in TTrees,...
Definition: RDataFrame.hxx:42
d
#define d(i)
Definition: RSha256.hxx:120