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df010_trivialDataSource.C File Reference

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Use the "trivial data source", an example data source implementation.

This tutorial illustrates how use the RDataFrame in combination with a RDataSource. In this case we use a RTrivialDS, which is nothing more than a simple generator: it does not interface to any existing dataset. The RTrivialDS has a single column, col0, which has value n for entry n. The code for RTrivialDS is available at these links (header and source):

Note that RTrivialDS is only a demo data source implementation and superior alternatives typically exist for production use (e.g. constructing an empty RDataFrame as RDataFrame(nEntries)).

auto nEvents = 128U;
auto d_s = ROOT::RDF::MakeTrivialDataFrame(nEvents);
/// Now we have a regular RDataFrame: the ingestion of data is delegated to
/// the RDataSource. At this point everything works as before.
auto h_s = d_s.Define("x", "1./(1. + col0)").Histo1D({"h_s", "h_s", 128, 0, .6}, "x");
/// Now we redo the same with a RDF from scratch and we draw the two histograms
ROOT::RDataFrame d(nEvents);
/// This lambda redoes what the RTrivialDS provides
auto g = []() {
static ULong64_t i = 0;
return i++;
auto h = d.Define("col0", g).Define("x", "1./(1. + col0)").Histo1D({"h", "h", 128, 0, .6}, "x");
auto c_s = new TCanvas();
auto c = new TCanvas();
return 0;
#define d(i)
Definition RSha256.hxx:102
#define c(i)
Definition RSha256.hxx:101
#define g(i)
Definition RSha256.hxx:105
#define h(i)
Definition RSha256.hxx:106
unsigned long long ULong64_t
Definition RtypesCore.h:81
ROOT's RDataFrame offers a modern, high-level interface for analysis of data stored in TTree ,...
The Canvas class.
Definition TCanvas.h:23
RInterface< RDFDetail::RLoopManager > MakeTrivialDataFrame()
Make a RDF wrapping a RTrivialDS with infinite entries, for demo purposes.
September 2017
Danilo Piparo (CERN)

Definition in file df010_trivialDataSource.C.