Re: [Boost-users] vectors with multiindex

From: Adán Cosgaya (acosgaya_at_[hidden])
Date: 2006-07-04 19:21:05

Hi,
tks for the answer,
and yes, my original idea was something along the lines of a vector of
vector, but what you described seem to be the right way to go.
would you mind giving me an example of how to insert some points (e.g. 4-d
or 5-d points), and iterate over them, I will need to access each point
during the next stage of my problem
Thanks

Adan

On 7/4/06, Joaquin M Lopez Munoz <joaquin_at_[hidden]> wrote:
>
> Hello Adán,
>
> Adán Cosgaya <acosgaya <at> gmail.com> writes:
> >
> > hi,i am new using the multiindex library, and I need to do the
> > following.I have a set of d-dimensional points (e.g (3,5,8,9,5)
> > is a 5-dimensional point), and I need to sort the points on
> > each of the coordinates.
> > I want to store the points in a vector,
>
> Do you mean that the points *are* vectors or that, moreover,
> they are stored in a vector (thus, a vector of vectors)?
> If the latter, why do you want to have them in a vector?
> Does not having them stored in the multi_index_container
> suffice? In the following I assume that the points are
> stored only in a multi_index_container whose first index is
> of type sequenced (std::list-like), which gives you the
> free-positioning interface you seem to need. If this is not
> what you're after please tell me so.
>
> > and use multiindex
> > to have all the points (vectors in this case) sorted in each of
> > the coordinates
> [...]
> > would you mind pointing me in the right direction with an
> > example of how to do it with multiindex library? thanks
>
> You only need to define an appropriate key extractor
> for the N-th element of a vector:
>
>   template<int N>
>   struct nth_coordinate
>   {
>     typedef int result_type;
>
>     int operator()(const std::vector<int>& x)const
>     {
>       return x[N]; // or .at(N) for greater safety
>     }
>   };
>
> so that the multi_index_container definition becomes:
>
>   typedef multi_index_container<
>     std::vector<int>,
>     indexed_by<
>       sequenced<>,
>       ordered_non_unique<nth_coordinate<0> >,
>       ordered_non_unique<nth_coordinate<1> >,
>       ordered_non_unique<nth_coordinate<2> >,
>       ordered_non_unique<nth_coordinate<3> >,
>       ordered_non_unique<nth_coordinate<4> >
>     >
>   > multi_index_t;
>
> Does this help? If for some reason the sequenced index
> at position #0 does not suffice, in Boost 1.34 there
> will be random access indices which are more similar
> to a vector, see http://tinyurl.com/psr6o .
>
> Good luck with your project,
>
> Joaquín M López Muñoz
> Telefónica, Investigación y Desarrollo
>
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