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
int df015_LazyDataSource()
{
auto fileNameUrl = "http://root.cern.ch/files/tutorials/df014_CsvDataSource_MuRun2010B.csv";
auto fileName = "df015_CsvDataSource_MuRun2010B.csv";
std::string px1Name = "px1";
auto px1 = csv_rdf.Take<double>(px1Name);
std::string py1Name = "py1";
auto py1 = csv_rdf.Take<double>(py1Name);
auto df =
MakeLazyDataFrame(std::make_pair(px1Name, px1), std::make_pair(py1Name, py1));
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");
can->SetLogy();
pt_h->DrawCopy();
return 0;
}
R__EXTERN TSystem * gSystem
virtual Bool_t Cp(const char *dst, Bool_t progressbar=kTRUE, UInt_t buffersize=1000000)
Allows to copy this file to the dst URL.
virtual Bool_t AccessPathName(const char *path, EAccessMode mode=kFileExists)
Returns FALSE if one can access a file using the specified access mode.
RDataFrame MakeLazyDataFrame(std::pair< std::string, RResultPtr< std::vector< ColumnTypes > > > &&... colNameProxyPairs)
Factory method to create a Lazy RDataFrame.
RDataFrame MakeCsvDataFrame(std::string_view fileName, bool readHeaders=true, char delimiter=',', Long64_t linesChunkSize=-1LL)
Factory method to create a CSV RDataFrame.
- Date
- February 2018
- Author
- Danilo Piparo
Definition in file df015_LazyDataSource.C.