RDataSource defines an API that RDataFrame can use to read arbitrary data formats.

A concrete RDataSource implementation (i.e. a class that inherits from RDataSource and implements all of its pure methods) provides an adaptor that RDataFrame can leverage to read any kind of tabular data formats. RDataFrame calls into RDataSource to retrieve information about the data, retrieve (thread-local) readers or "cursors" for selected columns and to advance the readers to the desired data entry.

The sequence of calls that RDataFrame (or any other client of a RDataSource) performs is the following:

SetNSlots() : inform RDataSource of the desired level of parallelism
GetColumnReaders() : retrieve from RDataSource per-thread readers for the desired columns
Initialize() : inform RDataSource that an event-loop is about to start
GetEntryRanges() : retrieve from RDataSource a set of ranges of entries that can be processed concurrently
InitSlot() : inform RDataSource that a certain thread is about to start working on a certain range of entries
SetEntry() : inform RDataSource that a certain thread is about to start working on a certain entry
FinalizeSlot() : inform RDataSource that a certain thread finished working on a certain range of entries
Finalize() : inform RDataSource that an event-loop finished

RDataSource implementations must support running multiple event-loops consecutively (although sequentially) on the same dataset.

SetNSlots() is called once per RDataSource object, typically when it is associated to a RDataFrame.
GetColumnReaders() can be called several times, potentially with the same arguments, also in-between event-loops, but not during an event-loop.
GetEntryRanges() will be called several times, including during an event loop, as additional ranges are needed. It will not be called concurrently.
Initialize() and Finalize() are called once per event-loop, right before starting and right after finishing.
InitSlot(), SetEntry(), and FinalizeSlot() can be called concurrently from multiple threads, multiple times per event-loop.

Advanced users that plan to implement a custom RDataSource can check out existing implementations, e.g. RCsvDS or RNTupleDS. See the inheritance diagram below for the full list of existing concrete implementations.

Definition at line 109 of file RDataSource.hxx.

Public Member Functions
virtual	~RDataSource ()=default

virtual void	Finalize ()
	Convenience method called after concluding an event-loop.

virtual void	FinalizeSlot (unsigned int)
	Convenience method called at the end of the data processing associated to a slot.

virtual const std::vector< std::string > &	GetColumnNames () const =0
	Returns a reference to the collection of the dataset's column names.

template<typename T >
std::vector< T ** >	GetColumnReaders (std::string_view columnName)
	Called at most once per column by RDF.

virtual std::unique_ptr< ROOT::Detail::RDF::RColumnReaderBase >	GetColumnReaders (unsigned int, std::string_view, const std::type_info &)
	If the other GetColumnReaders overload returns an empty vector, this overload will be called instead.

virtual std::vector< std::pair< ULong64_t, ULong64_t > >	GetEntryRanges ()=0
	Return ranges of entries to distribute to tasks.

virtual std::string	GetLabel ()
	Return a string representation of the datasource type.

virtual std::size_t	GetNFiles () const
	Returns the number of files from which the dataset is constructed.

virtual std::string	GetTypeName (std::string_view colName) const =0
	Type of a column as a string, e.g.

virtual bool	HasColumn (std::string_view colName) const =0
	Checks if the dataset has a certain column.

virtual void	Initialize ()
	Convenience method called before starting an event-loop.

virtual void	InitSlot (unsigned int, ULong64_t)
	Convenience method called at the start of the data processing associated to a slot.

virtual bool	SetEntry (unsigned int slot, ULong64_t entry)=0
	Advance the "cursors" returned by GetColumnReaders to the selected entry for a particular slot.

virtual void	SetNSlots (unsigned int nSlots)=0
	Inform RDataSource of the number of processing slots (i.e.

Protected Types
using	Record_t = std::vector< void * >

Protected Member Functions
virtual std::string	AsString ()

virtual Record_t	GetColumnReadersImpl (std::string_view name, const std::type_info &)=0
	type-erased vector of pointers to pointers to column values - one per slot

#include <ROOT/RDataSource.hxx>

Inheritance diagram for ROOT::RDF::RDataSource:

[legend]

Member Typedef Documentation

◆ Record_t

using ROOT::RDF::RDataSource::Record_t = std::vector<void *>

protected

Definition at line 112 of file RDataSource.hxx.

Constructor & Destructor Documentation

◆ ~RDataSource()

virtual ROOT::RDF::RDataSource::~RDataSource ( )

virtualdefault

Member Function Documentation

◆ AsString()

virtual std::string ROOT::RDF::RDataSource::AsString ( )

inlineprotectedvirtual

Reimplemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RCsvDS, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Internal::RDF::RRootDS, and ROOT::RDF::RTrivialDS.

Definition at line 115 of file RDataSource.hxx.

◆ Finalize()

virtual void ROOT::RDF::RDataSource::Finalize ( )

inlinevirtual

Convenience method called after concluding an event-loop.

See Initialize for more details.

Reimplemented in ROOT::RDF::RCsvDS, and ROOT::Experimental::RNTupleDS.

Definition at line 223 of file RDataSource.hxx.

◆ FinalizeSlot()

virtual void ROOT::RDF::RDataSource::FinalizeSlot ( unsigned int )

inlinevirtual

Convenience method called at the end of the data processing associated to a slot.

Parameters

[in] slot The data processing slot wihch needs to be finalized This method might be called multiple times per thread per event-loop.

Reimplemented in ROOT::Experimental::RNTupleDS, and ROOT::Internal::RDF::RRootDS.

Definition at line 217 of file RDataSource.hxx.

◆ GetColumnNames()

virtual const std::vector< std::string > & ROOT::RDF::RDataSource::GetColumnNames ( ) const

pure virtual

Returns a reference to the collection of the dataset's column names.

Implemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RArrowDS, ROOT::RDF::RCsvDS, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Experimental::RNTupleDS, ROOT::Internal::RDF::RRootDS, ROOT::RDF::RSqliteDS, and ROOT::RDF::RTrivialDS.

◆ GetColumnReaders() [1/2]

template<typename T >

std::vector< T ** > ROOT::RDF::RDataSource::GetColumnReaders ( std::string_view columnName )

inline

Called at most once per column by RDF.

Return vector of pointers to pointers to column values - one per slot.

Template Parameters

T	The type of the data stored in the column

Parameters

[in] columnName The name of the column

These pointers are veritable cursors: it's a responsibility of the RDataSource implementation that they point to the "right" memory region.

Definition at line 154 of file RDataSource.hxx.

◆ GetColumnReaders() [2/2]

virtual std::unique_ptr< ROOT::Detail::RDF::RColumnReaderBase > ROOT::RDF::RDataSource::GetColumnReaders	(	unsigned int	,
		std::string_view	,
		const std::type_info &
	)

inlinevirtual

If the other GetColumnReaders overload returns an empty vector, this overload will be called instead.

Parameters

[in]	slot	The data processing slot that needs to be considered
[in]	name	The name of the column for which a column reader needs to be returned
[in]	tid	A type_info At least one of the two must return a non-empty/non-null value.

Reimplemented in ROOT::Experimental::RNTupleDS.

Definition at line 169 of file RDataSource.hxx.

◆ GetColumnReadersImpl()

virtual Record_t ROOT::RDF::RDataSource::GetColumnReadersImpl	(	std::string_view	name,
		const std::type_info &
	)

protectedpure virtual

type-erased vector of pointers to pointers to column values - one per slot

Implemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Experimental::RNTupleDS, ROOT::RDF::RSqliteDS, ROOT::RDF::RTrivialDS, ROOT::RDF::RArrowDS, ROOT::RDF::RCsvDS, and ROOT::Internal::RDF::RRootDS.

◆ GetEntryRanges()

virtual std::vector< std::pair< ULong64_t, ULong64_t > > ROOT::RDF::RDataSource::GetEntryRanges ( )

pure virtual

Return ranges of entries to distribute to tasks.

They are required to be contiguous intervals with no entries skipped. Supposing a dataset with nEntries, the intervals must start at 0 and end at nEntries, e.g. [0-5],[5-10] for 10 entries. This function will be invoked repeatedly by RDataFrame as it needs additional entries to process. The same entry range should not be returned more than once. Returning an empty collection of ranges signals to RDataFrame that the processing can stop.

Implemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RArrowDS, ROOT::RDF::RCsvDS, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Experimental::RNTupleDS, ROOT::Internal::RDF::RRootDS, ROOT::RDF::RSqliteDS, and ROOT::RDF::RTrivialDS.

◆ GetLabel()

virtual std::string ROOT::RDF::RDataSource::GetLabel ( )

inlinevirtual

Return a string representation of the datasource type.

The returned string will be used by ROOT::RDF::SaveGraph() to represent the datasource in the visualization of the computation graph. Concrete datasources can override the default implementation.

Reimplemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RArrowDS, ROOT::RDF::RCsvDS, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Experimental::RNTupleDS, ROOT::Internal::RDF::RRootDS, ROOT::RDF::RSqliteDS, and ROOT::RDF::RTrivialDS.

Definition at line 229 of file RDataSource.hxx.

◆ GetNFiles()

virtual std::size_t ROOT::RDF::RDataSource::GetNFiles ( ) const

inlinevirtual

Returns the number of files from which the dataset is constructed.

Reimplemented in ROOT::RDF::RCsvDS, ROOT::Experimental::RNTupleDS, and ROOT::Internal::RDF::RRootDS.

Definition at line 128 of file RDataSource.hxx.

◆ GetTypeName()

virtual std::string ROOT::RDF::RDataSource::GetTypeName ( std::string_view colName ) const

pure virtual

Type of a column as a string, e.g.

GetTypeName("x") == "double". Required for jitting e.g. df.Filter("x>0").

Parameters

[in] colName The name of the column

Implemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RArrowDS, ROOT::RDF::RCsvDS, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Experimental::RNTupleDS, ROOT::Internal::RDF::RRootDS, ROOT::RDF::RSqliteDS, and ROOT::RDF::RTrivialDS.

◆ HasColumn()

virtual bool ROOT::RDF::RDataSource::HasColumn ( std::string_view colName ) const

pure virtual

Checks if the dataset has a certain column.

Parameters

[in] colName The name of the column

Implemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RArrowDS, ROOT::RDF::RCsvDS, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Experimental::RNTupleDS, ROOT::Internal::RDF::RRootDS, ROOT::RDF::RSqliteDS, and ROOT::RDF::RTrivialDS.

◆ Initialize()

virtual void ROOT::RDF::RDataSource::Initialize ( )

inlinevirtual

Convenience method called before starting an event-loop.

This method might be called multiple times over the lifetime of a RDataSource, since users can run multiple event-loops with the same RDataFrame. Ideally, Initialize should set the state of the RDataSource so that multiple identical event-loops will produce identical results.

Reimplemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RArrowDS, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Experimental::RNTupleDS, ROOT::Internal::RDF::RRootDS, ROOT::RDF::RSqliteDS, and ROOT::RDF::RTrivialDS.

Definition at line 202 of file RDataSource.hxx.

◆ InitSlot()

virtual void ROOT::RDF::RDataSource::InitSlot	(	unsigned int	,
		ULong64_t
	)

inlinevirtual

Convenience method called at the start of the data processing associated to a slot.

Parameters

[in]	slot	The data processing slot wihch needs to be initialized
[in]	firstEntry	The first entry of the range that the task will process. This method might be called multiple times per thread per event-loop.

Reimplemented in ROOT::RDF::RArrowDS, ROOT::Experimental::RNTupleDS, and ROOT::Internal::RDF::RRootDS.

Definition at line 210 of file RDataSource.hxx.

◆ SetEntry()

virtual bool ROOT::RDF::RDataSource::SetEntry	(	unsigned int	slot,
		ULong64_t	entry
	)

pure virtual

Advance the "cursors" returned by GetColumnReaders to the selected entry for a particular slot.

Parameters

[in]	slot	The data processing slot that needs to be considered
[in]	entry	The entry which needs to be pointed to by the reader pointers Slots are adopted to accommodate parallel data processing. Different workers will loop over different ranges and will be labelled by different "slot" values. Returns true if the entry has to be processed, false otherwise.

Implemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RArrowDS, ROOT::RDF::RCsvDS, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Internal::RDF::RRootDS, ROOT::RDF::RSqliteDS, ROOT::RDF::RTrivialDS, and ROOT::Experimental::RNTupleDS.

◆ SetNSlots()

virtual void ROOT::RDF::RDataSource::SetNSlots ( unsigned int nSlots )

pure virtual

Inform RDataSource of the number of processing slots (i.e.

worker threads) used by the associated RDataFrame. Slots numbers are used to simplify parallel execution: RDataFrame guarantees that different threads will always pass different slot values when calling methods concurrently.

Implemented in ROOT::Internal::RDF::RVecDS< ColumnTypes >, ROOT::RDF::RArrowDS, ROOT::RDF::RCsvDS, ROOT::RDF::RLazyDS< ColumnTypes >, ROOT::Experimental::RNTupleDS, ROOT::Internal::RDF::RRootDS, ROOT::RDF::RSqliteDS, and ROOT::RDF::RTrivialDS.

The documentation for this class was generated from the following file:

tree/dataframe/inc/ROOT/RDataSource.hxx

Public Member Functions

Protected Types

Protected Member Functions

Member Typedef Documentation

◆ Record_t

Constructor & Destructor Documentation

◆ ~RDataSource()

Member Function Documentation

◆ AsString()

◆ Finalize()

◆ FinalizeSlot()

◆ GetColumnNames()

◆ GetColumnReaders() [1/2]

◆ GetColumnReaders() [2/2]

◆ GetColumnReadersImpl()

◆ GetEntryRanges()

◆ GetLabel()

◆ GetNFiles()

◆ GetTypeName()

◆ HasColumn()

◆ Initialize()

◆ InitSlot()

◆ SetEntry()

◆ SetNSlots()