An RNTuple that is used to read data from storage.

An input ntuple provides data from storage as C++ objects. The ntuple model can be created from the data on storage or it can be imposed by the user. The latter case allows users to read into a specialized ntuple model that covers only a subset of the fields in the ntuple. The ntuple model is used when reading complete entries. Individual fields can be read as well by instantiating a tree view.

#include <ROOT/RNTupleReader.hxx>
using ROOT::Experimental::RNTupleReader;
 
#include <iostream>
 
auto ntuple = RNTupleReader::Open("myNTuple", "some/file.root");
std::cout << "myNTuple has " << ntuple->GetNEntries() << " entries\n";

Definition at line 71 of file RNTupleReader.hxx.

Classes
class	RIterator

Public Member Functions
	~RNTupleReader ()

RIterator	begin ()

std::unique_ptr< RNTupleReader >	Clone ()

void	EnableMetrics ()
	Enable performance measurements (decompression time, bytes read from storage, etc.)

RIterator	end ()

RNTupleCollectionView	GetCollectionView (DescriptorId_t fieldId)

RNTupleCollectionView	GetCollectionView (std::string_view fieldName)
	Raises an exception if:

const RNTupleDescriptor &	GetDescriptor ()
	Returns a cached copy of the page source descriptor.

template<typename T >
RNTupleDirectAccessView< T >	GetDirectAccessView (DescriptorId_t fieldId)

template<typename T >
RNTupleDirectAccessView< T >	GetDirectAccessView (std::string_view fieldName)

RNTupleGlobalRange	GetEntryRange ()
	Returns an iterator over the entry indices of the RNTuple.

const Detail::RNTupleMetrics &	GetMetrics () const

const RNTupleModel &	GetModel ()

NTupleSize_t	GetNEntries () const

template<typename T >
RNTupleView< T >	GetView (DescriptorId_t fieldId)

template<typename T >
RNTupleView< T >	GetView (DescriptorId_t fieldId, std::shared_ptr< T > objPtr)

template<typename T >
RNTupleView< T >	GetView (DescriptorId_t fieldId, T *rawPtr)

template<typename T >
RNTupleView< T >	GetView (std::string_view fieldName)
	Provides access to an individual field that can contain either a scalar value or a collection, e.g.

template<typename T >
RNTupleView< T >	GetView (std::string_view fieldName, std::shared_ptr< T > objPtr)

template<typename T >
RNTupleView< T >	GetView (std::string_view fieldName, T *rawPtr)

void	LoadEntry (NTupleSize_t index)
	Analogous to Fill(), fills the default entry of the model.

void	LoadEntry (NTupleSize_t index, REntry &entry)
	Fills a user provided entry after checking that the entry has been instantiated from the ntuple model.

void	PrintInfo (const ENTupleInfo what=ENTupleInfo::kSummary, std::ostream &output=std::cout) const
	Prints a detailed summary of the ntuple, including a list of fields.

void	Show (NTupleSize_t index, std::ostream &output=std::cout)
	Shows the values of the i-th entry/row, starting with 0 for the first entry.

Static Public Member Functions
static std::unique_ptr< RNTupleReader >	Open (const RNTuple &ntuple, const RNTupleReadOptions &options=RNTupleReadOptions())

static std::unique_ptr< RNTupleReader >	Open (std::string_view ntupleName, std::string_view storage, const RNTupleReadOptions &options=RNTupleReadOptions())
	Open an RNTuple for reading.

static std::unique_ptr< RNTupleReader >	Open (std::unique_ptr< RNTupleModel > model, const RNTuple &ntuple, const RNTupleReadOptions &options=RNTupleReadOptions())

static std::unique_ptr< RNTupleReader >	Open (std::unique_ptr< RNTupleModel > model, std::string_view ntupleName, std::string_view storage, const RNTupleReadOptions &options=RNTupleReadOptions())
	The caller imposes a model, which must be compatible with the model found in the data on storage.

static std::unique_ptr< RNTupleReader >	OpenFriends (std::span< RNTupleOpenSpec > ntuples, const RNTupleReadOptions &options=RNTupleReadOptions())
	Open RNTuples as one virtual, horizontally combined ntuple.

Private Member Functions
	RNTupleReader (std::unique_ptr< Internal::RPageSource > source, const RNTupleReadOptions &options)
	The model is generated from the ntuple metadata on storage.

	RNTupleReader (std::unique_ptr< RNTupleModel > model, std::unique_ptr< Internal::RPageSource > source, const RNTupleReadOptions &options)

void	ConnectModel (RNTupleModel &model)

RNTupleReader *	GetDisplayReader ()

void	InitPageSource (bool enableMetrics)

DescriptorId_t	RetrieveFieldId (std::string_view fieldName) const

Private Attributes
std::unique_ptr< RNTupleDescriptor >	fCachedDescriptor
	The ntuple descriptor in the page source is protected by a read-write lock.

std::unique_ptr< RNTupleReader >	fDisplayReader
	We use a dedicated on-demand reader for Show() and Scan().

Detail::RNTupleMetrics	fMetrics

std::unique_ptr< RNTupleModel >	fModel
	Needs to be destructed before fSource.

std::unique_ptr< Internal::RPageSource >	fSource

std::unique_ptr< Internal::RPageStorage::RTaskScheduler >	fUnzipTasks
	Set as the page source's scheduler for parallel page decompression if IMT is on Needs to be destructed after the pages source is destructed (an thus be declared before)

#include <ROOT/RNTupleReader.hxx>

Constructor & Destructor Documentation

◆ RNTupleReader() [1/2]

ROOT::Experimental::RNTupleReader::RNTupleReader	(	std::unique_ptr< RNTupleModel >	model,
		std::unique_ptr< Internal::RPageSource >	source,
		const RNTupleReadOptions &	options
	)

private

Definition at line 61 of file RNTupleReader.cxx.

◆ RNTupleReader() [2/2]

ROOT::Experimental::RNTupleReader::RNTupleReader	(	std::unique_ptr< Internal::RPageSource >	source,
		const RNTupleReadOptions &	options
	)

explicitprivate

The model is generated from the ntuple metadata on storage.

Definition at line 76 of file RNTupleReader.cxx.

◆ ~RNTupleReader()

ROOT::Experimental::RNTupleReader::~RNTupleReader ( )

default

Member Function Documentation

◆ begin()

RIterator ROOT::Experimental::RNTupleReader::begin ( )

inline

Definition at line 342 of file RNTupleReader.hxx.

◆ Clone()

std::unique_ptr< RNTupleReader > ROOT::Experimental::RNTupleReader::Clone ( )

inline

Definition at line 167 of file RNTupleReader.hxx.

◆ ConnectModel()

void ROOT::Experimental::RNTupleReader::ConnectModel ( RNTupleModel & model )

private

Definition at line 28 of file RNTupleReader.cxx.

◆ EnableMetrics()

void ROOT::Experimental::RNTupleReader::EnableMetrics ( )

inline

Enable performance measurements (decompression time, bytes read from storage, etc.)

Example: inspect the reader metrics after loading every entry

#include <ROOT/RNTupleReader.hxx>
using ROOT::Experimental::ENTupleInfo;
using ROOT::Experimental::RNTupleReader;
 
#include <iostream>
 
auto ntuple = RNTupleReader::Open("myNTuple", "some/file.root");
// metrics must be turned on beforehand
ntuple->EnableMetrics();
 
for (auto i : ntuple->GetEntryRange()) {
   ntuple->LoadEntry(i);
}
ntuple->PrintInfo(ENTupleInfo::kMetrics);

Definition at line 364 of file RNTupleReader.hxx.

◆ end()

RIterator ROOT::Experimental::RNTupleReader::end ( )

inline

Definition at line 343 of file RNTupleReader.hxx.

◆ GetCollectionView() [1/2]

RNTupleCollectionView ROOT::Experimental::RNTupleReader::GetCollectionView ( DescriptorId_t fieldId )

inline

Definition at line 337 of file RNTupleReader.hxx.

◆ GetCollectionView() [2/2]

RNTupleCollectionView ROOT::Experimental::RNTupleReader::GetCollectionView ( std::string_view fieldName )

inline

Raises an exception if:

there is no field with the given name or,
the field is not a collection

Definition at line 327 of file RNTupleReader.hxx.

◆ GetDescriptor()

const ROOT::Experimental::RNTupleDescriptor & ROOT::Experimental::RNTupleReader::GetDescriptor ( )

Returns a cached copy of the page source descriptor.

The returned pointer remains valid until the next call to LoadEntry or to any of the views returned from the reader.

Definition at line 230 of file RNTupleReader.cxx.

◆ GetDirectAccessView() [1/2]

template<typename T >

RNTupleDirectAccessView< T > ROOT::Experimental::RNTupleReader::GetDirectAccessView ( DescriptorId_t fieldId )

inline

Definition at line 317 of file RNTupleReader.hxx.

◆ GetDirectAccessView() [2/2]

template<typename T >

RNTupleDirectAccessView< T > ROOT::Experimental::RNTupleReader::GetDirectAccessView ( std::string_view fieldName )

inline

Definition at line 311 of file RNTupleReader.hxx.

◆ GetDisplayReader()

ROOT::Experimental::RNTupleReader * ROOT::Experimental::RNTupleReader::GetDisplayReader ( )

private

Definition at line 201 of file RNTupleReader.cxx.

◆ GetEntryRange()

RNTupleGlobalRange ROOT::Experimental::RNTupleReader::GetEntryRange ( )

inline

Returns an iterator over the entry indices of the RNTuple.

Example: iterate over all entries and print each entry in JSON format

#include <ROOT/RNTupleReader.hxx>
using ROOT::Experimental::ENTupleShowFormat;
using ROOT::Experimental::RNTupleReader;
 
#include <iostream>
 
auto ntuple = RNTupleReader::Open("myNTuple", "some/file.root");
for (auto i : ntuple->GetEntryRange()) {
   ntuple->Show(i);
}

Definition at line 246 of file RNTupleReader.hxx.

◆ GetMetrics()

const Detail::RNTupleMetrics & ROOT::Experimental::RNTupleReader::GetMetrics ( ) const

inline

Definition at line 365 of file RNTupleReader.hxx.

◆ GetModel()

const ROOT::Experimental::RNTupleModel & ROOT::Experimental::RNTupleReader::GetModel ( )

Definition at line 128 of file RNTupleReader.cxx.

◆ GetNEntries()

NTupleSize_t ROOT::Experimental::RNTupleReader::GetNEntries ( ) const

inline

Definition at line 175 of file RNTupleReader.hxx.

◆ GetView() [1/6]

template<typename T >

RNTupleView< T > ROOT::Experimental::RNTupleReader::GetView ( DescriptorId_t fieldId )

inline

Definition at line 287 of file RNTupleReader.hxx.

◆ GetView() [2/6]

template<typename T >

RNTupleView< T > ROOT::Experimental::RNTupleReader::GetView	(	DescriptorId_t	fieldId,
		std::shared_ptr< T >	objPtr
	)

inline

Definition at line 295 of file RNTupleReader.hxx.

◆ GetView() [3/6]

template<typename T >

RNTupleView< T > ROOT::Experimental::RNTupleReader::GetView	(	DescriptorId_t	fieldId,
		T *	rawPtr
	)

inline

Definition at line 303 of file RNTupleReader.hxx.

◆ GetView() [4/6]

template<typename T >

RNTupleView< T > ROOT::Experimental::RNTupleReader::GetView ( std::string_view fieldName )

inline

Provides access to an individual field that can contain either a scalar value or a collection, e.g.

GetView<double>("particles.pt") or GetView<std::vector<double>>("particle"). It can as well be the index field of a collection itself, like GetView<NTupleSize_t>("particle").

Raises an exception if there is no field with the given name.

Example: iterate over a field named "pt" of type float

#include <ROOT/RNTupleReader.hxx>
using ROOT::Experimental::RNTupleReader;
 
#include <iostream>
 
auto ntuple = RNTupleReader::Open("myNTuple", "some/file.root");
auto pt = ntuple->GetView<float>("pt");
 
for (auto i : ntuple->GetEntryRange()) {
   std::cout << i << ": " << pt(i) << "\n";
}

Definition at line 269 of file RNTupleReader.hxx.

◆ GetView() [5/6]

template<typename T >

RNTupleView< T > ROOT::Experimental::RNTupleReader::GetView	(	std::string_view	fieldName,
		std::shared_ptr< T >	objPtr
	)

inline

Definition at line 275 of file RNTupleReader.hxx.

◆ GetView() [6/6]

template<typename T >

RNTupleView< T > ROOT::Experimental::RNTupleReader::GetView	(	std::string_view	fieldName,
		T *	rawPtr
	)

inline

Definition at line 281 of file RNTupleReader.hxx.

◆ InitPageSource()

void ROOT::Experimental::RNTupleReader::InitPageSource ( bool enableMetrics )

private

Definition at line 46 of file RNTupleReader.cxx.

◆ LoadEntry() [1/2]

void ROOT::Experimental::RNTupleReader::LoadEntry ( NTupleSize_t index )

inline

Analogous to Fill(), fills the default entry of the model.

Returns false at the end of the ntuple. On I/O errors, raises an exception.

Definition at line 219 of file RNTupleReader.hxx.

◆ LoadEntry() [2/2]

void ROOT::Experimental::RNTupleReader::LoadEntry	(	NTupleSize_t	index,
		REntry &	entry
	)

inline

Fills a user provided entry after checking that the entry has been instantiated from the ntuple model.

Definition at line 229 of file RNTupleReader.hxx.

◆ Open() [1/4]

std::unique_ptr< ROOT::Experimental::RNTupleReader > ROOT::Experimental::RNTupleReader::Open	(	const RNTuple &	ntuple,
		const RNTupleReadOptions &	options = `RNTupleReadOptions()`
	)

static

Definition at line 102 of file RNTupleReader.cxx.

◆ Open() [2/4]

std::unique_ptr< ROOT::Experimental::RNTupleReader > ROOT::Experimental::RNTupleReader::Open	(	std::string_view	ntupleName,
		std::string_view	storage,
		const RNTupleReadOptions &	options = `RNTupleReadOptions()`
	)

static

Open an RNTuple for reading.

Throws an RException if there is no RNTuple with the given name.

Example: open an RNTuple and print the number of entries

#include <ROOT/RNTupleReader.hxx>
using ROOT::Experimental::RNTupleReader;
 
#include <iostream>
 
auto ntuple = RNTupleReader::Open("myNTuple", "some/file.root");
std::cout << "myNTuple has " << ntuple->GetNEntries() << " entries\n";

Definition at line 94 of file RNTupleReader.cxx.

◆ Open() [3/4]

std::unique_ptr< ROOT::Experimental::RNTupleReader > ROOT::Experimental::RNTupleReader::Open	(	std::unique_ptr< RNTupleModel >	model,
		const RNTuple &	ntuple,
		const RNTupleReadOptions &	options = `RNTupleReadOptions()`
	)

static

Definition at line 109 of file RNTupleReader.cxx.

◆ Open() [4/4]

std::unique_ptr< ROOT::Experimental::RNTupleReader > ROOT::Experimental::RNTupleReader::Open	(	std::unique_ptr< RNTupleModel >	model,
		std::string_view	ntupleName,
		std::string_view	storage,
		const RNTupleReadOptions &	options = `RNTupleReadOptions()`
	)

static

The caller imposes a model, which must be compatible with the model found in the data on storage.

Definition at line 86 of file RNTupleReader.cxx.

◆ OpenFriends()

std::unique_ptr< ROOT::Experimental::RNTupleReader > ROOT::Experimental::RNTupleReader::OpenFriends	(	std::span< RNTupleOpenSpec >	ntuples,
		const RNTupleReadOptions &	options = `RNTupleReadOptions()`
	)

static

Open RNTuples as one virtual, horizontally combined ntuple.

The underlying RNTuples must have an identical number of entries. Fields in the combined RNTuple are named with the ntuple name as a prefix, e.g. myNTuple1.px and myNTuple2.pt (see tutorial ntpl006_friends)

Definition at line 117 of file RNTupleReader.cxx.

◆ PrintInfo()

void ROOT::Experimental::RNTupleReader::PrintInfo	(	const ENTupleInfo	what = `ENTupleInfo::kSummary`,
		std::ostream &	output = `std::cout`
	)		const

Prints a detailed summary of the ntuple, including a list of fields.

Example: print summary information to stdout

#include <ROOT/RNTupleReader.hxx>
using ROOT::Experimental::ENTupleInfo;
using ROOT::Experimental::RNTupleReader;
 
#include <iostream>
 
auto ntuple = RNTupleReader::Open("myNTuple", "some/file.root");
ntuple->PrintInfo();
// or, equivalently:
ntuple->PrintInfo(ENTupleInfo::kSummary, std::cout);

Example: print detailed column storage data to stderr

#include <ROOT/RNTupleReader.hxx>
using ROOT::Experimental::ENTupleInfo;
using ROOT::Experimental::RNTupleReader;
 
#include <iostream>
 
auto ntuple = RNTupleReader::Open("myNTuple", "some/file.root");
ntuple->PrintInfo(ENTupleInfo::kStorageDetails, std::cerr);

For use of ENTupleInfo::kMetrics, see EnableMetrics.

Definition at line 137 of file RNTupleReader.cxx.

◆ RetrieveFieldId()

ROOT::Experimental::DescriptorId_t ROOT::Experimental::RNTupleReader::RetrieveFieldId ( std::string_view fieldName ) const

private

Definition at line 238 of file RNTupleReader.cxx.

◆ Show()

void ROOT::Experimental::RNTupleReader::Show	(	NTupleSize_t	index,
		std::ostream &	output = `std::cout`
	)

Shows the values of the i-th entry/row, starting with 0 for the first entry.

By default, prints the output in JSON format. Uses the visitor pattern to traverse through each field of the given entry.

Definition at line 208 of file RNTupleReader.cxx.

Member Data Documentation

◆ fCachedDescriptor

std::unique_ptr<RNTupleDescriptor> ROOT::Experimental::RNTupleReader::fCachedDescriptor

private

The ntuple descriptor in the page source is protected by a read-write lock.

We don't expose that to the users of RNTupleReader::GetDescriptor(). Instead, if descriptor information is needed, we clone the descriptor. Using the descriptor's generation number, we know if the cached descriptor is stale. Retrieving descriptor data from an RNTupleReader is supposed to be for testing and information purposes, not on a hot code path.

Definition at line 89 of file RNTupleReader.hxx.

◆ fDisplayReader

std::unique_ptr<RNTupleReader> ROOT::Experimental::RNTupleReader::fDisplayReader

private

We use a dedicated on-demand reader for Show() and Scan().

Printing data uses all the fields from the full model even if the analysis code uses only a subset of fields. The display reader is a clone of the original reader.

Definition at line 83 of file RNTupleReader.hxx.

◆ fMetrics

Detail::RNTupleMetrics ROOT::Experimental::RNTupleReader::fMetrics

private

Definition at line 90 of file RNTupleReader.hxx.

◆ fModel

std::unique_ptr<RNTupleModel> ROOT::Experimental::RNTupleReader::fModel

private

Needs to be destructed before fSource.

Definition at line 79 of file RNTupleReader.hxx.

◆ fSource

std::unique_ptr<Internal::RPageSource> ROOT::Experimental::RNTupleReader::fSource

private

Definition at line 77 of file RNTupleReader.hxx.

◆ fUnzipTasks

std::unique_ptr<Internal::RPageStorage::RTaskScheduler> ROOT::Experimental::RNTupleReader::fUnzipTasks

private

Set as the page source's scheduler for parallel page decompression if IMT is on Needs to be destructed after the pages source is destructed (an thus be declared before)

Definition at line 75 of file RNTupleReader.hxx.

Libraries for ROOT::Experimental::RNTupleReader:

[legend]

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

tree/ntuple/v7/inc/ROOT/RNTupleReader.hxx
tree/ntuple/v7/src/RNTupleReader.cxx

Classes

Public Member Functions

Static Public Member Functions

Private Member Functions

Private Attributes

Constructor & Destructor Documentation

◆ RNTupleReader() [1/2]

◆ RNTupleReader() [2/2]

◆ ~RNTupleReader()

Member Function Documentation

◆ begin()

◆ Clone()

◆ ConnectModel()

◆ EnableMetrics()

◆ end()

◆ GetCollectionView() [1/2]

◆ GetCollectionView() [2/2]

◆ GetDescriptor()

◆ GetDirectAccessView() [1/2]

◆ GetDirectAccessView() [2/2]

◆ GetDisplayReader()

◆ GetEntryRange()

◆ GetMetrics()

◆ GetModel()

◆ GetNEntries()

◆ GetView() [1/6]

◆ GetView() [2/6]

◆ GetView() [3/6]

◆ GetView() [4/6]

◆ GetView() [5/6]

◆ GetView() [6/6]

◆ InitPageSource()

◆ LoadEntry() [1/2]

◆ LoadEntry() [2/2]

◆ Open() [1/4]

◆ Open() [2/4]

◆ Open() [3/4]

◆ Open() [4/4]

◆ OpenFriends()

◆ PrintInfo()

◆ RetrieveFieldId()

◆ Show()

Member Data Documentation

◆ fCachedDescriptor

◆ fDisplayReader

◆ fMetrics

◆ fModel

◆ fSource

◆ fUnzipTasks