Re: Proposed algorithm library: reduce, combine, filter, guard

From: farrow_at_[hidden]
Date: 2001-08-09 15:24:54

Alexander, Gary, George,

Thanks for the informative replies.

Doesn't look like combine exists, exactly the way I wanted, but
accumulate seems kinda close.  I'm happy to 'plug away' for now.

Rob Farrow
farrow_at_[hidden]

--- In boost_at_y..., Gary Powell <Gary.Powell_at_s...> wrote:
> [Rob Farrow]
> Using STL algorithms...
> I am unable to deduce a way of combining or reducing sequence
> containers into a single result or filtering arbitrary iterators
with
> a predicate.  So I have created these...
> 
> REDUCE: applies a binary operator where the first argument is the
> current intermediate result and the second is each value in the
> sequence.  The result of each function application becomes the new
> result.
> 
> Example:
> 
> vector<int> nums; //contains { 1, 2, 3 }
> int result = reduce(nums.begin(), nums.end(), plus<int>(), 0);
> //result = 6
> 
> [Gary Powell]
>   int result = std::accumulate(nums.begin(), nums.end(), 0,
plus<int>());
> 
> 
> FILTER: a wrapper for an iterator that applies a predicate functor.
> The resulting iterator only stops at objects that pass the
predicate.
> 
> vector<int> nums; //contains { 1, 15, 2, 10, 3 }
> int result = reduce(filter(nums.begin(),
>                            bind2nd(less_than<int>(),10)),
>                     nums.end(), plus<int>(), 0);
> //result = 6
> [Gary Powell]
> 
>    vtl::filter_view<vector<int>, int(*)() > filter(nums,
> bind2nd(less_than<int>(),10));
> 
>   result = std::accumulate(filter.begin(), filter.end(), 0,
plus<int>() );
> 
> or use a boost::filter_iterator_generator.
> 
>    
> 
> GUARD: is the complement of FILTER.
> The resulting iterator only stops at objects that FAIL the
predicate.
> 
> [Gary Powell]
> Just reverse the test.
> 
> 
> 
>   Just some alternatives.
> 
>   Yours,
>  -gary-