acts_examples::GroupBy< Iterator, KeyGetter > Class Template Reference

Proxy for iterating over groups of elements within a container. More...

#include <GroupBy.h>

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
	Iterator type representing the end of the groups.

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

Private Attributes
Iterator	m_begin_
Iterator	m_end_
KeyGetter	m_key_getter_

Detailed Description

template<typename Iterator, typename KeyGetter>
class acts_examples::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.h.

Member Typedef Documentation

Group

template<typename Iterator , typename KeyGetter >

using acts_examples::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.h.

GroupEndIterator

template<typename Iterator , typename KeyGetter >

using acts_examples::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.h.

Key

template<typename Iterator , typename KeyGetter >

using acts_examples::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.h.

Constructor & Destructor Documentation

GroupBy()

template<typename Iterator , typename KeyGetter >

acts_examples::GroupBy< Iterator, KeyGetter >::GroupBy ( Iterator begin, Iterator end, KeyGetter keyGetter = KeyGetter() )

inlineconstexpr

Construct the group-by proxy for an iterator range.

Definition at line 102 of file GroupBy.h.

      : m_begin_(begin), m_end_(end), m_key_getter_(std::move(keyGetter)) {}

Member Function Documentation

begin()

template<typename Iterator , typename KeyGetter >

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

inlineconstexpr

Definition at line 105 of file GroupBy.h.

                                        {
    return GroupIterator(*this, m_begin_);
  }

empty()

template<typename Iterator , typename KeyGetter >

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

inlineconstexpr

Definition at line 109 of file GroupBy.h.

{ return m_begin_ == m_end_; }

end()

template<typename Iterator , typename KeyGetter >

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

inlineconstexpr

Definition at line 108 of file GroupBy.h.

{ return m_end_; }

findEndOfGroup()

template<typename Iterator , typename KeyGetter >

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

inlineconstexprprivate

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.h.

                                                          {
    // check for end so we can safely dereference the start iterator.
    if (start == m_end_) {
      return start;
    }
    // search the first element that does not share a key with the start.
    return std::find_if_not(std::next(start), m_end_,
                            [this, start](const auto& x_) {
                              return m_key_getter_(x_) == m_key_getter_(*start);
                            });
  }

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

Member Data Documentation

m_begin_

template<typename Iterator , typename KeyGetter >

Iterator acts_examples::GroupBy< Iterator, KeyGetter >::m_begin_

private

Definition at line 112 of file GroupBy.h.

m_end_

template<typename Iterator , typename KeyGetter >

Iterator acts_examples::GroupBy< Iterator, KeyGetter >::m_end_

private

Definition at line 113 of file GroupBy.h.

m_key_getter_

template<typename Iterator , typename KeyGetter >

KeyGetter acts_examples::GroupBy< Iterator, KeyGetter >::m_key_getter_

private

Definition at line 114 of file GroupBy.h.

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

• Tracking/include/Tracking/Sim/GroupBy.h