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- [/ File gather.qbk]
- [section:gather gather]
- [/license
- Copyright (c) 2013 Marshall Clow
- Distributed under the Boost Software License, Version 1.0.
- (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
- ]
- The header file 'boost/algorithm/gather.hpp' contains two variants of a single algorithm, `gather`.
- `gather()` takes a collection of elements defined by a pair of iterators and moves the ones satisfying a predicate to them to a position (called the pivot) within the sequence. The algorithm is stable. The result is a pair of iterators that contains the items that satisfy the predicate.
- [heading Interface]
- The function `gather` returns a `std::pair` of iterators that denote the elements that satisfy the predicate.
- There are two versions; one takes two iterators, and the other takes a range.
- ``
- namespace boost { namespace algorithm {
- template <typename BidirectionalIterator, typename Pred>
- std::pair<BidirectionalIterator,BidirectionalIterator>
- gather ( BidirectionalIterator first, BidirectionalIterator last, BidirectionalIterator pivot, Pred pred );
- template <typename BidirectionalRange, typename Pred>
- std::pair<typename boost::range_iterator<const BidirectionalRange>::type, typename boost::range_iterator<const BidirectionalRange>::type>
- gather ( const BidirectionalRange &range, typename boost::range_iterator<const BidirectionalRange>::type pivot, Pred pred );
- }}
- ``
- [heading Examples]
- Given an sequence containing:
- ``
- 0 1 2 3 4 5 6 7 8 9
- ``
- a call to gather ( arr, arr + 10, arr + 4, IsEven ) will result in:
- ``
- 1 3 0 2 4 6 8 5 7 9
- |---|-----|
- first | second
- pivot
- ``
- where `first` and `second` are the fields of the pair that is returned by the call.
- [heading Iterator Requirements]
- `gather` work on bidirectional iterators or better. This requirement comes from the usage of `stable_partition`, which requires bidirectional iterators. Some standard libraries (libstdc++ and libc++, for example) have implementations of `stable_partition` that work with forward iterators. If that is the case, then `gather` will work with forward iterators as well.
- [heading Storage Requirements]
- `gather` uses `stable_partition`, which will attempt to allocate temporary memory, but will work in-situ if there is none available.
- [heading Complexity]
- If there is sufficient memory available, the run time is linear: `O(N)`
- If there is not any memory available, then the run time is `O(N log N)`.
- [heading Exception Safety]
- [heading Notes]
- [endsect]
- [/ File gather.qbk
- Copyright 2013 Marshall Clow
- Distributed under the Boost Software License, Version 1.0.
- (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt).
- ]
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