#include <acts/blob/master/Examples/Framework/include/ACTFW/Utilities/GroupBy.hpp>

Classes
class	GroupIterator
	Iterator type representing a group of elements. More...

Public Types
using	Key = std::decay_t< decltype(KeyGetter()(*Iterator()))>
	The key type that identifies elements within a group.

using	Group = std::pair< Key, Range< Iterator >>
	A Group is an iterator range with the associated key.

using	GroupEndIterator = Iterator

Public Member Functions
constexpr	GroupBy (Iterator begin, Iterator end, KeyGetter keyGetter=KeyGetter())
	Construct the group-by proxy for an iterator range.

constexpr GroupIterator	begin () const

constexpr GroupEndIterator	end () const

constexpr bool	empty () const

Private Member Functions
constexpr Iterator	findEndOfGroup (Iterator start) const

Private Attributes
Iterator	m_begin

Iterator	m_end

KeyGetter	m_keyGetter

Detailed Description

template<typename Iterator, typename KeyGetter>
class FW::GroupBy< Iterator, KeyGetter >

Proxy for iterating over groups of elements within a container.

Note: Each group will contain at least one element.

Consecutive elements with the same key (as defined by the KeyGetter) are placed in one group. The proxy should always be used as part of a range-based for loop. In combination with structured bindings to reduce the boilerplate, the group iteration can be written as

for (auto&& [key, elements] : GroupBy<...>(...)) {
    // do something with just the key
    ...

    // iterate over the group elements
    for (const auto& element : elements) {
        ...
    }

Definition at line 39 of file GroupBy.hpp.

View newest version in sPHENIX GitHub at line 39 of file GroupBy.hpp

Member Typedef Documentation

template<typename Iterator , typename KeyGetter >

using FW::GroupBy< Iterator, KeyGetter >::Group = std::pair<Key, Range<Iterator>>

A Group is an iterator range with the associated key.

Definition at line 44 of file GroupBy.hpp.

View newest version in sPHENIX GitHub at line 44 of file GroupBy.hpp

template<typename Iterator , typename KeyGetter >

using FW::GroupBy< Iterator, KeyGetter >::GroupEndIterator = Iterator

Iterator type representing the end of the groups.

The end iterator will not be dereferenced in C++17 range-based loops. It can thus be a simpler type without the overhead of the full group iterator below.

Definition at line 50 of file GroupBy.hpp.

View newest version in sPHENIX GitHub at line 50 of file GroupBy.hpp

template<typename Iterator , typename KeyGetter >

using FW::GroupBy< Iterator, KeyGetter >::Key = std::decay_t<decltype(KeyGetter()(*Iterator()))>

The key type that identifies elements within a group.

Definition at line 42 of file GroupBy.hpp.

View newest version in sPHENIX GitHub at line 42 of file GroupBy.hpp

Constructor & Destructor Documentation

template<typename Iterator , typename KeyGetter >

constexpr FW::GroupBy< Iterator, KeyGetter >::GroupBy	(	Iterator	begin,
		Iterator	end,
		KeyGetter	keyGetter = `KeyGetter()`
	)

inline

Construct the group-by proxy for an iterator range.

Definition at line 102 of file GroupBy.hpp.

View newest version in sPHENIX GitHub at line 102 of file GroupBy.hpp

Member Function Documentation

template<typename Iterator , typename KeyGetter >

constexpr GroupIterator FW::GroupBy< Iterator, KeyGetter >::begin ( ) const

inline

Definition at line 105 of file GroupBy.hpp.

View newest version in sPHENIX GitHub at line 105 of file GroupBy.hpp

References FW::GroupBy< Iterator, KeyGetter >::m_begin.

template<typename Iterator , typename KeyGetter >

constexpr bool FW::GroupBy< Iterator, KeyGetter >::empty ( ) const

inline

Definition at line 109 of file GroupBy.hpp.

View newest version in sPHENIX GitHub at line 109 of file GroupBy.hpp

References FW::GroupBy< Iterator, KeyGetter >::m_begin, and FW::GroupBy< Iterator, KeyGetter >::m_end.

template<typename Iterator , typename KeyGetter >

constexpr GroupEndIterator FW::GroupBy< Iterator, KeyGetter >::end ( ) const

inline

Definition at line 108 of file GroupBy.hpp.

View newest version in sPHENIX GitHub at line 108 of file GroupBy.hpp

References FW::GroupBy< Iterator, KeyGetter >::m_end.

template<typename Iterator , typename KeyGetter >

constexpr Iterator FW::GroupBy< Iterator, KeyGetter >::findEndOfGroup ( Iterator start ) const

inlineprivate

Find the end of the group that starts at the given position.

This uses a linear search from the start position and thus has linear complexity in the group size. It does not assume any ordering of the underlying container and is a cache-friendly access pattern.

Definition at line 121 of file GroupBy.hpp.

View newest version in sPHENIX GitHub at line 121 of file GroupBy.hpp

References FW::GroupBy< Iterator, KeyGetter >::m_end, FW::GroupBy< Iterator, KeyGetter >::m_keyGetter, start(), and x.

Referenced by FW::GroupBy< Iterator, KeyGetter >::GroupIterator::operator++().

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