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/RNTuple.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 101 of file RNTuple.hxx.

Classes
class	RIterator

struct	ROpenSpec
	Used to specify the underlying RNTuples in OpenFriends() More...

Public Member Functions
	RNTupleReader (std::unique_ptr< Detail::RPageSource > source)
	The model is generated from the ntuple metadata on storage.

	RNTupleReader (std::unique_ptr< RNTupleModel > model, std::unique_ptr< Detail::RPageSource > source)
	The user imposes an ntuple model, which must be compatible with the model found in the data on storage.

	~RNTupleReader ()

RIterator	begin ()

std::unique_ptr< RNTupleReader >	Clone ()

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

RIterator	end ()

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

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

const Detail::RNTupleMetrics &	GetMetrics () const

RNTupleModel *	GetModel ()

NTupleSize_t	GetNEntries () const

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.

RNTupleViewCollection	GetViewCollection (std::string_view fieldName)
	Raises an exception if:

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)
	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 (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, std::string_view ntupleName, std::string_view storage, const RNTupleReadOptions &options=RNTupleReadOptions())
	Throws an exception if the model is null.

static std::unique_ptr< RNTupleReader >	OpenFriends (std::span< ROpenSpec > ntuples)
	Open RNTuples as one virtual, horizontally combined ntuple.

Private Member Functions
void	ConnectModel (const RNTupleModel &model)

RNTupleReader *	GetDisplayReader ()

void	InitPageSource ()

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< Detail::RPageSource >	fSource

std::unique_ptr< Detail::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/RNTuple.hxx>

Constructor & Destructor Documentation

◆ RNTupleReader() [1/2]

ROOT::Experimental::RNTupleReader::RNTupleReader	(	std::unique_ptr< RNTupleModel >	model,
		std::unique_ptr< Detail::RPageSource >	source
	)

The user imposes an ntuple model, which must be compatible with the model found in the data on storage.

Throws an exception if the model or the source is null.

Definition at line 94 of file RNTuple.cxx.

◆ RNTupleReader() [2/2]

ROOT::Experimental::RNTupleReader::RNTupleReader ( std::unique_ptr< Detail::RPageSource > source )

explicit

The model is generated from the ntuple metadata on storage.

Throws an exception if the source is null.

Definition at line 112 of file RNTuple.cxx.

◆ ~RNTupleReader()

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

default

Member Function Documentation

◆ begin()

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

inline

Definition at line 320 of file RNTuple.hxx.

◆ Clone()

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

inline

Definition at line 199 of file RNTuple.hxx.

◆ ConnectModel()

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

private

Definition at line 67 of file RNTuple.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/RNTuple.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 342 of file RNTuple.hxx.

◆ end()

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

inline

Definition at line 321 of file RNTuple.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 255 of file RNTuple.cxx.

◆ GetDisplayReader()

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

private

Definition at line 226 of file RNTuple.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/RNTuple.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 276 of file RNTuple.hxx.

◆ GetMetrics()

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

inline

Definition at line 343 of file RNTuple.hxx.

◆ GetModel()

ROOT::Experimental::RNTupleModel * ROOT::Experimental::RNTupleReader::GetModel ( )

Definition at line 153 of file RNTuple.cxx.

◆ GetNEntries()

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

inline

Definition at line 203 of file RNTuple.hxx.

◆ GetView()

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/RNTuple.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 299 of file RNTuple.hxx.

◆ GetViewCollection()

RNTupleViewCollection ROOT::Experimental::RNTupleReader::GetViewCollection ( 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 311 of file RNTuple.hxx.

◆ InitPageSource()

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

private

Definition at line 82 of file RNTuple.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 246 of file RNTuple.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 255 of file RNTuple.hxx.

◆ Open() [1/3]

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

static

Definition at line 138 of file RNTuple.cxx.

◆ Open() [2/3]

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/RNTuple.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 131 of file RNTuple.cxx.

◆ Open() [3/3]

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

Throws an exception if the model is null.

Definition at line 124 of file RNTuple.cxx.

◆ OpenFriends()

std::unique_ptr< ROOT::Experimental::RNTupleReader > ROOT::Experimental::RNTupleReader::OpenFriends ( std::span< ROpenSpec > ntuples )

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 144 of file RNTuple.cxx.

◆ PrintInfo()

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

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

Example: print summary information to stdout

#include <ROOT/RNTuple.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/RNTuple.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 162 of file RNTuple.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 233 of file RNTuple.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 119 of file RNTuple.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 113 of file RNTuple.hxx.

◆ fMetrics

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

private

Definition at line 120 of file RNTuple.hxx.

◆ fModel

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

private

Needs to be destructed before fSource.

Definition at line 109 of file RNTuple.hxx.

◆ fSource

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

private

Definition at line 107 of file RNTuple.hxx.

◆ fUnzipTasks

std::unique_ptr<Detail::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 105 of file RNTuple.hxx.

Libraries for ROOT::Experimental::RNTupleReader:

[legend]

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

tree/ntuple/v7/inc/ROOT/RNTuple.hxx
tree/ntuple/v7/src/RNTuple.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()

◆ GetDescriptor()

◆ GetDisplayReader()

◆ GetEntryRange()

◆ GetMetrics()

◆ GetModel()

◆ GetNEntries()

◆ GetView()

◆ GetViewCollection()

◆ InitPageSource()

◆ LoadEntry() [1/2]

◆ LoadEntry() [2/2]

◆ Open() [1/3]

◆ Open() [2/3]

◆ Open() [3/3]

◆ OpenFriends()

◆ PrintInfo()

◆ Show()

Member Data Documentation

◆ fCachedDescriptor

◆ fDisplayReader

◆ fMetrics

◆ fModel

◆ fSource

◆ fUnzipTasks