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Reference Guide
df010_trivialDataSource.C File Reference

Detailed Description

View in nbviewer Open in SWAN This tutorial illustrates how use the RDataFrame in combination with a RDataSource.

In this case we use a TTrivialDS, which is nothing more than a simple generator: it does not interface to any existing dataset. The TTrivialDS has a single column, col0, which has value n for entry n.

{
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 TTrivialDS 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();
c_s->SetLogy();
h_s->DrawClone();
auto c = new TCanvas();
c->SetLogy();
h->DrawClone();
return 0;
}
Date
September 2017
Author
Danilo Piparo

Definition in file df010_trivialDataSource.C.