df015_LazyDataSource¶
Use the lazy RDataFrame data source to concatenate computation graphs.
This tutorial illustrates how to take advantage of a lazy data source creating a data frame from columns of one or multiple parent dataframe(s), delaying the creation of the columns to the actual usage of the daughter data frame. Dataset Reference: McCauley, T. (2014). Dimuon event information derived from the Run2010B public Mu dataset. CERN Open Data Portal. DOI: 10.7483/OPENDATA.CMS.CB8H.MFFA. From the ROOT website: https://root.cern.ch/files/tutorials/tdf014_CsvDataSource_MuRun2010B.csv
Author: Danilo Piparo (CERN)
This notebook tutorial was automatically generated with ROOTBOOK-izer from the macro found in the ROOT repository on Monday, March 27, 2023 at 09:45 AM.
using namespace ROOT::RDF;
Let's first create a RDF that will read from the CSV file. See the tutorial (https://root.cern.ch/doc/master/df014__CSVDataSource_8C.html) on CSV data sources for more details!
auto fileNameUrl = "http://root.cern.ch/files/tutorials/df014_CsvDataSource_MuRun2010B.csv";
auto fileName = "df015_CsvDataSource_MuRun2010B.csv";
if(gSystem->AccessPathName(fileName))
TFile::Cp(fileNameUrl, fileName);
auto csv_rdf = FromCSV(fileName);
[TFile::Cp] Total 14.46 MB |====================| 100.00 % [198.1 MB/s]
Now we take out two columns: px and py of the first muon in the muon pair
std::string px1Name = "px1";
auto px1 = csv_rdf.Take<double>(px1Name);
std::string py1Name = "py1";
auto py1 = csv_rdf.Take<double>(py1Name);
Now we create a new dataframe built on top of the columns above. Note that up to now, no event loop has been carried out!
auto df = MakeLazyDataFrame(std::make_pair(px1Name, px1), std::make_pair(py1Name, py1));
We build a histogram of the transverse momentum of the muons.
auto ptFormula = [](double px, double py) { return sqrt(px * px + py * py); };
auto pt_h = df.Define("pt", ptFormula, {"px1", "py1"})
.Histo1D<double>({"pt", "Muon p_{T};p_{T} [GeV/c];", 128, 0, 128}, "pt");
auto can = new TCanvas();
can->SetLogy();
pt_h->DrawCopy();
return 0;
Draw all canvases
gROOT->GetListOfCanvases()->Draw()
