遍历一系列范围 [英] Iterating over a range of ranges
问题描述
如果我有一系列的范围,是有办法一起加入他们的行列,并遍历他们,如果他们是一个单一的范围是多少?
If I have a range of ranges, is there a way to join them together and iterate over them as if they were a single range?
按范围,我的意思是任何类型的容器或迭代器对。基本上像升压的范围。提升已经具备了功能与增强连接两个范围::一起加入,但该功能不能加入范围的arbitary数量。
By range, I mean any kind of container or iterator pair. Basically like boost's ranges. Boost already have a function for joining two ranges together with boost::join, but that function can't join an arbitary number of ranges.
基本上,我正在寻找一个方式做什么的多
函数确实在这片code的:
Basically, I'm looking for a way to do what the the many
function does in this piece of code:
std::vector<std::vector<int>> n = {{0, 1}, {2, 3}};
for (auto i : many(n))
std::cout << i << '\n';
其中将输出0,1,2,3
Which would output 0, 1, 2, 3.
在C#中,我有的SelectMany
这可能做到这一点。
In C#, I had SelectMany
which could do this.
推荐答案
下面是与基于范围(摘自<二手不上不下迭代器的例子href=\"http://stackoverflow.com/questions/11783541/c-iterator-adapter-over-collection-of-vectors?lq=1\">here并加入的boost :: make_iterator_range
显示范围版)(仍需要工作虽然):
Here is an example of a flattening iterator used with range-based for (taken from here and added boost::make_iterator_range
to show range version) (still needs work though):
#include <boost/iterator/iterator_adaptor.hpp>
#include <boost/range.hpp>
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <string>
#include <utility>
template <typename Iter>
class flattening_iterator :
public boost::iterator_adaptor<
flattening_iterator<Iter>,
Iter,
typename Iter::value_type::iterator::value_type,
boost::forward_traversal_tag,
typename Iter::value_type::iterator::value_type
>
{
private:
using super_t = boost::iterator_adaptor<
flattening_iterator<Iter>,
Iter,
typename Iter::value_type::iterator::value_type,
boost::forward_traversal_tag,
typename Iter::value_type::iterator::value_type
>;
using inner_iterator = typename Iter::value_type::iterator;
public:
flattening_iterator(Iter it)
: super_t(it),
inner_begin(),
inner_end(),
outer_end(it)
{}
flattening_iterator(Iter begin, Iter end)
: super_t(begin),
inner_begin((*begin).begin()),
inner_end((*begin).end()),
outer_end(end)
{}
using value_type = typename Iter::value_type::iterator::value_type;
private:
friend class boost::iterator_core_access;
inner_iterator inner_begin;
inner_iterator inner_end;
Iter outer_end;
void increment()
{
if (this->base_reference() == outer_end)
return; // At the end
++inner_begin;
if (inner_begin == inner_end)
{
++this->base_reference();
inner_begin = (*this->base_reference()).begin();
inner_end = (*this->base_reference()).end();
}
}
value_type dereference() const
{
return *inner_begin;
}
};
template <typename Iter>
auto flat_iter(Iter it) -> flattening_iterator<Iter>
{
return flattening_iterator<Iter>(it);
}
template <typename Iter>
auto flat_iter(Iter begin, Iter end) -> flattening_iterator<Iter>
{
return flattening_iterator<Iter>(begin, end);
}
template <typename Cont>
auto flatten(Cont& c) -> boost::iterator_range<flattening_iterator<decltype(std::declval<Cont>().begin())>>
{
return boost::make_iterator_range(flat_iter(c.begin(), c.end()), flat_iter(c.end()));
}
int main()
{
std::vector<std::vector<int>> v1{{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
for (auto i : flatten(v1))
{
std::cout << i << ' ';
}
}
输出
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
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