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Reference Guide
df011_ROOTDataSource.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 RRootDS. This data source allows to read a ROOT dataset from a RDataFrame in a different way, not based on the regular RDataFrame code. This allows to perform all sorts of consistency checks and illustrate the usage of the RDataSource in a didactic context.

void fill_tree(const char *treeName, const char *fileName)
auto i = 0.;
d.Define("b1", [&i]() { return i++; }).Snapshot(treeName, fileName);
auto fileName = "df011_ROOTDataSources.root";
auto treeName = "myTree";
fill_tree(treeName, fileName);
auto d_s = ROOT::RDF::MakeRootDataFrame(treeName, fileName);
/// 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./(b1 + 1.)").Histo1D({"h_s", "h_s", 128, 0, .6}, "x");
/// Now we redo the same with a RDF and we draw the two histograms
ROOT::RDataFrame d(treeName, fileName);
auto h = d.Define("x", "1./(b1 + 1.)").Histo1D({"h", "h", 128, 0, .6}, "x");
auto c_s = new TCanvas();
auto c = new TCanvas();
return 0;
September 2017
Danilo Piparo

Definition in file df011_ROOTDataSource.C.