template<typename T>
class ROOT::VecOps::RVec< T >

A "std::vector"-like collection of values implementing handy operation to analyse them.

Template Parameters

T	The type of the contained objects

A RVec is a container designed to make analysis of values' collections fast and easy. Its storage is contiguous in memory and its interface is designed such to resemble to the one of the stl vector. In addition the interface features methods and external functions to ease the manipulation and analysis of the data in the RVec.

Note

ROOT::VecOps::RVec can also be spelled simply ROOT::RVec. Shorthand aliases such as ROOT::RVecI or ROOT::RVecD are also available as template instantiations of RVec of fundamental types. The full list of available aliases:

RVecB (bool)
RVecC (char)
RVecD (double)
RVecF (float)
RVecI (int)
RVecL (long)
RVecLL (long long)
RVecU (unsigned)
RVecUL (unsigned long)
RVecULL (unsigned long long)

RVec does not attempt to be exception safe. Exceptions thrown by element constructors during insertions, swaps or other operations will be propagated potentially leaving the RVec object in an invalid state.

RVec methods (e.g. at or size) follow the STL naming convention instead of the ROOT naming convention in order to make RVec a drop-in replacement for std::vector.

Example

Suppose to have an event featuring a collection of muons with a certain pseudorapidity, momentum and charge, e.g.:

std::vector<short> mu_charge {1, 1, -1, -1, -1, 1, 1, -1};
std::vector<float> mu_pt {56, 45, 32, 24, 12, 8, 7, 6.2};
std::vector<float> mu_eta {3.1, -.2, -1.1, 1, 4.1, 1.6, 2.4, -.5};

Suppose you want to extract the transverse momenta of the muons satisfying certain criteria, for example consider only negatively charged muons with a pseudorapidity smaller or equal to 2 and with a transverse momentum greater than 10 GeV. Such a selection would require, among the other things, the management of an explicit loop, for example:

std::vector<float> goodMuons_pt;
const auto size = mu_charge.size();
for (size_t i=0; i < size; ++i) {
   if (mu_pt[i] > 10 && abs(mu_eta[i]) <= 2. &&  mu_charge[i] == -1) {
      goodMuons_pt.emplace_back(mu_pt[i]);
   }
}

These operations become straightforward with RVec - we just need to write what we mean:

auto goodMuons_pt = mu_pt[ (mu_pt > 10.f && abs(mu_eta) <= 2.f && mu_charge == -1) ]

Now the clean collection of transverse momenta can be used within the rest of the data analysis, for example to fill a histogram.

Owning and adopting memory

RVec has contiguous memory associated to it. It can own it or simply adopt it. In the latter case, it can be constructed with the address of the memory associated to it and its length. For example:

std::vector<int> myStlVec {1,2,3};

RVec<int> myRVec(myStlVec.data(), myStlVec.size());

ROOT::VecOps::RVec

A "std::vector"-like collection of values implementing handy operation to analyse them.

Definition RVec.hxx:1480

In this case, the memory associated to myStlVec and myRVec is the same, myRVec simply "adopted it". If any method which implies a re-allocation is called, e.g. emplace_back or resize, the adopted memory is released and new one is allocated. The previous content is copied in the new memory and preserved.

Sorting and manipulation of indices

Sorting

RVec complies to the STL interfaces when it comes to iterations. As a result, standard algorithms can be used, for example sorting:

RVec<double> v{6., 4., 5.};

std::sort(v.begin(), v.end());

v

@ v

Definition rootcling_impl.cxx:3661

For convenience, helpers are provided too:

auto sorted_v = Sort(v);

auto reversed_v = Reverse(v);

ROOT::VecOps::Reverse

RVec< T > Reverse(const RVec< T > &v)

Return copy of reversed vector.

Definition RVec.hxx:2391

ROOT::VecOps::Sort

RVec< T > Sort(const RVec< T > &v)

Return copy of RVec with elements sorted in ascending order.

Definition RVec.hxx:2412

Manipulation of indices

It is also possible to manipulated the RVecs acting on their indices. For example, the following syntax

RVecD v0 {9., 7., 8.};

auto v1 = Take(v0, {1, 2, 0});

ROOT::VecOps::Take

RVec< T > Take(const RVec< T > &v, const RVec< typename RVec< T >::size_type > &i)

Return elements of a vector at given indices.

Definition RVec.hxx:2287

v0

@ v0

Definition rootcling_impl.cxx:3662

v1

@ v1

Definition rootcling_impl.cxx:3663

will yield a new RVec<double> the content of which is the first, second and zeroth element of v0, i.e. {7., 8., 9.}.

The Argsort and StableArgsort helper extracts the indices which order the content of a RVec. For example, this snippet accomplishes in a more expressive way what we just achieved:

auto v1_indices = Argsort(v0); // The content of v1_indices is {1, 2, 0}.

v1 = Take(v0, v1_indices);

ROOT::VecOps::Argsort

RVec< typename RVec< T >::size_type > Argsort(const RVec< T > &v)

Return an RVec of indices that sort the input RVec.

Definition RVec.hxx:2198

The Take utility allows to extract portions of the RVec. The content to be taken can be specified with an RVec of indices or an integer. If the integer is negative, elements will be picked starting from the end of the container:

RVecF vf {1.f, 2.f, 3.f, 4.f};
auto vf_1 = Take(vf, {1, 3}); // The content is {2.f, 4.f}
auto vf_2 = Take(vf, 2); // The content is {1.f, 2.f}
auto vf_3 = Take(vf, -3); // The content is {2.f, 3.f, 4.f}

Usage in combination with RDataFrame

RDataFrame leverages internally RVecs. Suppose to have a dataset stored in a TTree which holds these columns (here we choose C arrays to represent the collections, they could be as well std::vector instances):

nPart            "nPart/I"            An integer representing the number of particles
px               "px[nPart]/D"        The C array of the particles' x component of the momentum
py               "py[nPart]/D"        The C array of the particles' y component of the momentum
E                "E[nPart]/D"         The C array of the particles' Energy

Suppose you'd like to plot in a histogram the transverse momenta of all particles for which the energy is greater than 200 MeV. The code required would just be:

RDataFrame d("mytree", "myfile.root");
auto cutPt = [](RVecD &pxs, RVecD &pys, RVecD &Es) {
   auto all_pts = sqrt(pxs * pxs + pys * pys);
   auto good_pts = all_pts[Es > 200.];
   return good_pts;
   };
 
auto hpt = d.Define("pt", cutPt, {"px", "py", "E"})
            .Histo1D("pt");
hpt->Draw();

And if you'd like to express your selection as a string:

RDataFrame d("mytree", "myfile.root");
auto hpt = d.Define("pt", "sqrt(pxs * pxs + pys * pys)[E>200]")
            .Histo1D("pt");
hpt->Draw();

PyROOT

The ROOT::RVec class has additional features in Python, which allow to adopt memory from Numpy arrays and vice versa. The purpose of these features is the copyless interfacing of Python and C++ using their most common data containers, Numpy arrays and RVec with a std::vector interface.

Conversion of RVecs to Numpy arrays

RVecs of fundamental types (int, float, ...) have in Python the __array_interface__ attribute attached. This information allows Numpy to adopt the memory of RVecs without copying the content. You can find further documentation regarding the Numpy array interface here. The following code example demonstrates the memory adoption mechanism using numpy.asarray.

rvec = ROOT.RVec('double')((1, 2, 3))
print(rvec) # { 1.0000000, 2.0000000, 3.0000000 }
 
npy = numpy.asarray(rvec)
print(npy) # [1. 2. 3.]
 
rvec[0] = 42
print(npy) # [42. 2. 3.]

Conversion of Numpy arrays to RVecs

Data owned by Numpy arrays with fundamental types (int, float, ...) can be adopted by RVecs. To create an RVec from a Numpy array, ROOT offers the facility ROOT.VecOps.AsRVec, which performs a similar operation to numpy.asarray, but vice versa. A code example demonstrating the feature and the adoption of the data owned by the Numpy array is shown below.

npy = numpy.array([1.0, 2.0, 3.0])
print(npy) # [1. 2. 3.]
 
rvec = ROOT.VecOps.AsRVec(npy)
print(rvec) # { 1.0000000, 2.0000000, 3.0000000 }
 
npy[0] = 42
print(rvec) # { 42.000000, 2.0000000, 3.0000000 }

Definition at line 1480 of file RVec.hxx.

Public Types
using	const_reference = typename SuperClass::const_reference

using	reference = typename SuperClass::reference

using	size_type = typename SuperClass::size_type

using	value_type = typename SuperClass::value_type

Public Types inherited from ROOT::VecOps::RVecN< T, Internal::VecOps::RVecInlineStorageSize< T >::value >
using	const_reference = typename Internal::VecOps::SmallVectorTemplateCommon< T >::const_reference

using	reference = typename Internal::VecOps::SmallVectorTemplateCommon< T >::reference

using	size_type = typename Internal::VecOps::SmallVectorTemplateCommon< T >::size_type

using	value_type = typename Internal::VecOps::SmallVectorTemplateCommon< T >::value_type

Public Types inherited from ROOT::Detail::VecOps::RVecImpl< T >
using	const_iterator = typename SuperClass::const_iterator

using	iterator = typename SuperClass::iterator

using	reference = typename SuperClass::reference

using	size_type = typename SuperClass::size_type

Public Types inherited from ROOT::Internal::VecOps::SmallVectorTemplateCommon< T >
using	const_iterator = const T *

using	const_pointer = const T *

using	const_reference = const T &

using	const_reverse_iterator = std::reverse_iterator< const_iterator >

using	difference_type = ptrdiff_t

using	iterator = T *

using	pointer = T *

using	reference = T &

using	reverse_iterator = std::reverse_iterator< iterator >

using	size_type = size_t

using	value_type = T

Public Types inherited from ROOT::Internal::VecOps::SmallVectorBase
using	Size_T = int32_t

Public Member Functions
	RVec ()

	RVec (const RVec &RHS)

template<unsigned N>
	RVec (const RVecN< T, N > &RHS)

	RVec (const std::vector< T > &RHS)

	RVec (Detail::VecOps::RVecImpl< T > &&RHS)

template<typename ItTy , typename = typename std::enable_if<std::is_convertible< typename std::iterator_traits<ItTy>::iterator_category, std::input_iterator_tag>::value>::type>
	RVec (ItTy S, ItTy E)

	RVec (RVec &&RHS)

template<unsigned N>
	RVec (RVecN< T, N > &&RHS)

	RVec (size_t Size)

	RVec (size_t Size, const T &Value)

	RVec (std::initializer_list< T > IL)

	RVec (T *p, size_t n)

template<typename U , typename = std::enable_if<std::is_convertible<T, U>::value>>
	operator RVec () const

RVec &	operator= (const RVec &RHS)

RVec &	operator= (RVec &&RHS)

template<typename V , typename = std::enable_if<std::is_convertible<V, bool>::value>>
RVec	operator[] (const RVec< V > &conds) const

Public Member Functions inherited from ROOT::VecOps::RVecN< T, Internal::VecOps::RVecInlineStorageSize< T >::value >
	RVecN ()

	RVecN (const RVecN &RHS)

	RVecN (const std::vector< T > &RHS)

	RVecN (Detail::VecOps::RVecImpl< T > &&RHS)

	RVecN (ItTy S, ItTy E)

	RVecN (RVecN &&RHS)

	RVecN (size_t Size)

	RVecN (size_t Size, const T &Value)

	RVecN (std::initializer_list< T > IL)

	RVecN (T *p, size_t n)

	~RVecN ()

reference	at (size_type pos)

const_reference	at (size_type pos) const

value_type	at (size_type pos, value_type fallback)
	No exception thrown. The user specifies the desired value in case the RVecN is shorter than `pos`.

value_type	at (size_type pos, value_type fallback) const
	No exception thrown. The user specifies the desired value in case the RVecN is shorter than `pos`.

	operator RVecN< U, M > () const

RVecN &	operator= (const RVecN &RHS)

RVecN &	operator= (Detail::VecOps::RVecImpl< T > &&RHS)

RVecN &	operator= (RVecN &&RHS)

RVecN &	operator= (std::initializer_list< T > IL)

RVecN	operator[] (const RVecN< V, M > &conds) const

reference	operator[] (size_type idx)

const_reference	operator[] (size_type idx) const

Public Member Functions inherited from ROOT::Detail::VecOps::RVecImpl< T >
	RVecImpl (const RVecImpl &)=delete

	~RVecImpl ()

template<typename in_iter , typename = typename std::enable_if<std::is_convertible< typename std::iterator_traits<in_iter>::iterator_category, std::input_iterator_tag>::value>::type>
void	append (in_iter in_start, in_iter in_end)
	Add the specified range to the end of the SmallVector.

void	append (size_type NumInputs, const T &Elt)
	Append `NumInputs` copies of `Elt` to the end.

void	append (std::initializer_list< T > IL)

template<typename in_iter , typename = typename std::enable_if<std::is_convertible< typename std::iterator_traits<in_iter>::iterator_category, std::input_iterator_tag>::value>::type>
void	assign (in_iter in_start, in_iter in_end)

void	assign (size_type NumElts, const T &Elt)

void	assign (std::initializer_list< T > IL)

void	clear ()

template<typename... ArgTypes>
reference	emplace_back (ArgTypes &&...Args)

iterator	erase (const_iterator CI)

iterator	erase (const_iterator CS, const_iterator CE)

iterator	insert (iterator I, const T &Elt)

template<typename ItTy , typename = typename std::enable_if<std::is_convertible< typename std::iterator_traits<ItTy>::iterator_category, std::input_iterator_tag>::value>::type>
iterator	insert (iterator I, ItTy From, ItTy To)

iterator	insert (iterator I, size_type NumToInsert, const T &Elt)

void	insert (iterator I, std::initializer_list< T > IL)

iterator	insert (iterator I, T &&Elt)

RVecImpl &	operator= (const RVecImpl &RHS)

RVecImpl &	operator= (RVecImpl &&RHS)

void	pop_back_n (size_type NumItems)

T	pop_back_val ()

void	reserve (size_type N)

void	resize (size_type N)

void	resize (size_type N, const T &NV)

void	swap (RVecImpl &RHS)

Public Member Functions inherited from ROOT::Internal::VecOps::SmallVectorTemplateBase< T, bool >
void	pop_back ()

void	push_back (const T &Elt)

void	push_back (T &&Elt)

Public Member Functions inherited from ROOT::Internal::VecOps::SmallVectorTemplateCommon< T >
reference	back ()

const_reference	back () const

const_iterator	begin () const noexcept

iterator	begin () noexcept

size_t	capacity () const noexcept

size_t	capacity_in_bytes () const

const_iterator	cbegin () const noexcept

const_iterator	cend () const noexcept

const_reverse_iterator	crbegin () const noexcept

const_reverse_iterator	crend () const noexcept

const_pointer	data () const noexcept
	Return a pointer to the vector's buffer, even if empty().

pointer	data () noexcept
	Return a pointer to the vector's buffer, even if empty().

bool	empty () const

const_iterator	end () const noexcept

iterator	end () noexcept

reference	front ()

const_reference	front () const

size_type	max_size () const noexcept

const_reverse_iterator	rbegin () const noexcept

reverse_iterator	rbegin () noexcept

const_reverse_iterator	rend () const noexcept

reverse_iterator	rend () noexcept

size_t	size () const

size_type	size_in_bytes () const

Public Member Functions inherited from ROOT::Internal::VecOps::SmallVectorBase
size_t	capacity () const noexcept

bool	empty () const

void	set_size (size_t N)
	Set the array size to `N`, which the current array must have enough capacity for.

size_t	size () const

Private Types
using	SuperClass = RVecN< T, Internal::VecOps::RVecInlineStorageSize< T >::value >

Friends
bool	ROOT::Detail::VecOps::IsAdopting (const RVec< T > &v)

bool	ROOT::Detail::VecOps::IsSmall (const RVec< T > &v)

Additional Inherited Members
Protected Member Functions inherited from ROOT::Detail::VecOps::RVecImpl< T >
	RVecImpl (unsigned N)

Protected Member Functions inherited from ROOT::Internal::VecOps::SmallVectorTemplateBase< T, bool >
	SmallVectorTemplateBase (size_t Size)

void	grow (size_t MinSize=0)
	Grow the allocated memory (without initializing new elements), doubling the size of the allocated memory.

Protected Member Functions inherited from ROOT::Internal::VecOps::SmallVectorTemplateCommon< T >
	SmallVectorTemplateCommon (size_t Size)

void	grow_pod (size_t MinSize, size_t TSize)

bool	isSmall () const
	Return true if this is a smallvector which has not had dynamic memory allocated for it.

void	resetToSmall ()
	Put this vector in a state of being small.

Protected Member Functions inherited from ROOT::Internal::VecOps::SmallVectorBase
	SmallVectorBase ()=delete

	SmallVectorBase (void *FirstEl, size_t TotalCapacity)

void	grow_pod (void *FirstEl, size_t MinSize, size_t TSize)
	This is an implementation of the grow() method which only works on POD-like data types and is out of line to reduce code duplication.

bool	Owns () const
	If true, the RVec is in "memory adoption" mode, i.e. it is acting as a view on a memory buffer it does not own.

Static Protected Member Functions inherited from ROOT::Internal::VecOps::SmallVectorTemplateBase< T, bool >
static void	destroy_range (T S, T E)

template<typename It1 , typename It2 >
static void	uninitialized_copy (It1 I, It1 E, It2 Dest)
	Copy the range [I, E) onto the uninitialized memory starting with "Dest", constructing elements as needed.

template<typename It1 , typename It2 >
static void	uninitialized_move (It1 I, It1 E, It2 Dest)
	Move the range [I, E) into the uninitialized memory starting with "Dest", constructing elements as needed.

Static Protected Member Functions inherited from ROOT::Internal::VecOps::SmallVectorBase
static void	report_at_maximum_capacity ()
	Report that this vector is already at maximum capacity.

static void	report_size_overflow (size_t MinSize)
	Report that MinSize doesn't fit into this vector's size type.

static constexpr size_t	SizeTypeMax ()
	The maximum value of the Size_T used.

Protected Attributes inherited from ROOT::Internal::VecOps::SmallVectorBase
void *	fBeginX

Size_T	fCapacity
	Always >= -1. fCapacity == -1 indicates the RVec is in "memory adoption" mode.

Size_T	fSize = 0
	Always >= 0.

#include <ROOT/RVec.hxx>

Inheritance diagram for ROOT::VecOps::RVec< T >:

[legend]

Member Typedef Documentation

◆ const_reference

template<typename T >

using ROOT::VecOps::RVec< T >::const_reference = typename SuperClass::const_reference

Definition at line 1484 of file RVec.hxx.

◆ reference

template<typename T >

using ROOT::VecOps::RVec< T >::reference = typename SuperClass::reference

Definition at line 1483 of file RVec.hxx.

◆ size_type

template<typename T >

using ROOT::VecOps::RVec< T >::size_type = typename SuperClass::size_type

Definition at line 1485 of file RVec.hxx.

◆ SuperClass

template<typename T >

using ROOT::VecOps::RVec< T >::SuperClass = RVecN<T, Internal::VecOps::RVecInlineStorageSize<T>::value>

private

Definition at line 1481 of file RVec.hxx.

◆ value_type

template<typename T >

using ROOT::VecOps::RVec< T >::value_type = typename SuperClass::value_type

Definition at line 1486 of file RVec.hxx.

Constructor & Destructor Documentation

◆ RVec() [1/12]

template<typename T >

ROOT::VecOps::RVec< T >::RVec ( )

inline

Definition at line 1490 of file RVec.hxx.

◆ RVec() [2/12]

template<typename T >

ROOT::VecOps::RVec< T >::RVec	(	size_t	Size,
		const T &	Value
	)

inlineexplicit

Definition at line 1492 of file RVec.hxx.

◆ RVec() [3/12]

template<typename T >

ROOT::VecOps::RVec< T >::RVec ( size_t Size )

inlineexplicit

Definition at line 1494 of file RVec.hxx.

◆ RVec() [4/12]

template<typename T >

template<typename ItTy , typename = typename std::enable_if<std::is_convertible< typename std::iterator_traits<ItTy>::iterator_category, std::input_iterator_tag>::value>::type>

ROOT::VecOps::RVec< T >::RVec	(	ItTy	S,
		ItTy	E
	)

inline

Definition at line 1499 of file RVec.hxx.

◆ RVec() [5/12]

template<typename T >

ROOT::VecOps::RVec< T >::RVec ( std::initializer_list< T > IL )

inline

Definition at line 1503 of file RVec.hxx.

◆ RVec() [6/12]

template<typename T >

ROOT::VecOps::RVec< T >::RVec ( const RVec< T > & RHS )

inline

Definition at line 1505 of file RVec.hxx.

◆ RVec() [7/12]

template<typename T >

ROOT::VecOps::RVec< T >::RVec ( RVec< T > && RHS )

inline

Definition at line 1513 of file RVec.hxx.

◆ RVec() [8/12]

template<typename T >

ROOT::VecOps::RVec< T >::RVec ( Detail::VecOps::RVecImpl< T > && RHS )

inline

Definition at line 1521 of file RVec.hxx.

◆ RVec() [9/12]

template<typename T >

template<unsigned N>

ROOT::VecOps::RVec< T >::RVec ( RVecN< T, N > && RHS )

inline

Definition at line 1524 of file RVec.hxx.

◆ RVec() [10/12]

template<typename T >

template<unsigned N>

ROOT::VecOps::RVec< T >::RVec ( const RVecN< T, N > & RHS )

inline

Definition at line 1527 of file RVec.hxx.

◆ RVec() [11/12]

template<typename T >

ROOT::VecOps::RVec< T >::RVec ( const std::vector< T > & RHS )

inline

Definition at line 1529 of file RVec.hxx.

◆ RVec() [12/12]

template<typename T >

ROOT::VecOps::RVec< T >::RVec	(	T *	p,
		size_t	n
	)

inline

Definition at line 1531 of file RVec.hxx.

Member Function Documentation

◆ operator RVec()

template<typename T >

template<typename U , typename = std::enable_if<std::is_convertible<T, U>::value>>

ROOT::VecOps::RVec< T >::operator RVec ( ) const

inline

Definition at line 1535 of file RVec.hxx.

◆ operator=() [1/2]

template<typename T >

RVec & ROOT::VecOps::RVec< T >::operator= ( const RVec< T > & RHS )

inline

Definition at line 1507 of file RVec.hxx.

◆ operator=() [2/2]

template<typename T >

RVec & ROOT::VecOps::RVec< T >::operator= ( RVec< T > && RHS )

inline

Definition at line 1515 of file RVec.hxx.

◆ operator[]()

template<typename T >

template<typename V , typename = std::enable_if<std::is_convertible<V, bool>::value>>

RVec ROOT::VecOps::RVec< T >::operator[] ( const RVec< V > & conds ) const

inline

Definition at line 1543 of file RVec.hxx.

Friends And Related Symbol Documentation

◆ ROOT::Detail::VecOps::IsAdopting

template<typename T >

bool ROOT::Detail::VecOps::IsAdopting ( const RVec< T > & v )

friend

◆ ROOT::Detail::VecOps::IsSmall

template<typename T >

bool ROOT::Detail::VecOps::IsSmall ( const RVec< T > & v )

friend

core/cont/inc/TCollectionProxyInfo.h

math/vecops/inc/ROOT/RVec.hxx

Table of Contents

Example

Owning and adopting memory

Sorting and manipulation of indices

Sorting

Manipulation of indices

Usage in combination with RDataFrame

PyROOT

Conversion of RVecs to Numpy arrays

Conversion of Numpy arrays to RVecs

Public Types

Public Member Functions

Private Types

Friends

Additional Inherited Members

Member Typedef Documentation

◆ const_reference

◆ reference

◆ size_type

◆ SuperClass

◆ value_type

Constructor & Destructor Documentation

◆ RVec() [1/12]

◆ RVec() [2/12]

◆ RVec() [3/12]

◆ RVec() [4/12]

◆ RVec() [5/12]

◆ RVec() [6/12]

◆ RVec() [7/12]

◆ RVec() [8/12]

◆ RVec() [9/12]

◆ RVec() [10/12]

◆ RVec() [11/12]

◆ RVec() [12/12]

Member Function Documentation

◆ operator RVec()

◆ operator=() [1/2]

◆ operator=() [2/2]

◆ operator[]()

Friends And Related Symbol Documentation

◆ ROOT::Detail::VecOps::IsAdopting

◆ ROOT::Detail::VecOps::IsSmall