Re: [Boost-users] ranking of ublas vector

Subject: Re: [Boost-users] ranking of ublas vector
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-03-13 16:18:27

AMDG

Kraus Philipp wrote:
> I have a very large non sparse ublas vector (most long double content).
> I would like to sort this vector without change the vector content, but
> I know the rank of the elements like
>
> the smalest element in the vector is the 312 element in the original
> vector (for example).
>
> Is there a boost implementation for create ranking of elements?

There isn't, but it's fairly straightforward to do.

ublas::vector<long double> vec;

using namespace boost::lambda;
std::vector<std::size_t> temp(boost::counting_iterator<std::size_t>(0), 
boost::counting_iterator<std::size_t>(vec.size()));
std::sort(temp.begin(), temp.end(), var(vec)[_1] < var(vec)[_2]);
std::vector<std::size_t> ranking(temp.size());
std::copy(boost::counting_iterator<std::size_t>(0), 
boost::counting_iterator<std::size_t>(vec.size()),
    boost::make_permutation_iterator(ranking.begin(), temp.begin()));

In Christ,
Steven Watanabe