vector indices

[slurper]

tx for answer Bazarov

i have another problem

i have a vector with 20 elements in it (20 ints).

i'd like to have the elements sorted in ascending order, but somehow i need
to know what index the element was at in the original vector.

someone?
tx for quick and good answers so far

[Jon Bell]

In article <41***********************@news.skynet.be>,
slurper <sl*********@skynet.be> wrote:

i have a vector with 20 elements in it (20 ints).

i'd like to have the elements sorted in ascending order, but somehow i need
to know what index the element was at in the original vector.

Create a second vector of 20 ints, and initialize it so it elements are
the same as the indexes, i.e. v2[0] == 0, v2[1] === 1, etc. Let's call
this an "index vector".

Write a sort function using your favorite sort algorithm. Whenever you
move alements around in the data vector in the process of sorting it (such
as swap two elements), do the same thing to the corresponding elements of
the index vector.

After this function executes, the element at position k of the data vector
will have originally been in position v2[k] of the unsorted data vector.

--
Jon Bell <jt*******@presby.edu> Presbyterian College
Dept. of Physics and Computer Science Clinton, South Carolina USA

[Rob Williscroft]

slurper wrote in news:41***********************@news.skynet.be in
comp.lang.c++:

tx for answer Bazarov

i have another problem

i have a vector with 20 elements in it (20 ints).

i'd like to have the elements sorted in ascending order, but somehow i
need to know what index the element was at in the original vector.

someone?
tx for quick and good answers so far

#include <cstdlib>
#include <utility>
#include <vector>
#include <algorithm>

std::vector< std::pair< int, std::size_t > >
sort_and_index( std::vector< int > const &in )
{
std::vector< std::pair< int, std::size_t > > out( in.size() );

for ( std::size_t i = 0; i < in.size(); ++i )
{
out[ i ].first = in[ i ];
out[ i ].second = i;
}

std::sort( out.begin(), out.end() );

return out;
}

Rob.
--
http://www.victim-prime.dsl.pipex.com/

[@(none)]

Maybe something like this (probably overkill but hey STL is fun)...

#include<map>
#include<set>
#include<vector>

typedef std::vector<int> iVec_t;
typedef iVec_t::iterator iVec_i;
typedef std::set<int> iSet_t;
typedef std::map<int,iSet_t> isMap_t;

iVec_t data;

// load and populate data with your data

isMap_t indicies;

for( iVec_i di = data.begin() ; di != data.end() ; ++di )
indicies[*di].insert(di-data.begin());

std::sort(data.begin(),data.end());

// Now you have sorted data, and the indicies map will map
// your data values to a set of indicies in the original
// vector where that data was found.
// The set in the map allows for data values to appear more
// than once in the original vector.
slurper wrote:

tx for answer Bazarov

i have another problem

i have a vector with 20 elements in it (20 ints).

i'd like to have the elements sorted in ascending order, but somehow i need
to know what index the element was at in the original vector.

someone?
tx for quick and good answers so far

[Phil Staite]

Maybe something like this (probably overkill but hey STL is fun)...

#include<map>
#include<set>
#include<vector>

typedef std::vector<int> iVec_t;
typedef iVec_t::iterator iVec_i;
typedef std::set<int> iSet_t;
typedef std::map<int,iSet_t> isMap_t;

iVec_t data;

// load and populate data with your data

isMap_t indicies;

for( iVec_i di = data.begin() ; di != data.end() ; ++di )
indicies[*di].insert(di-data.begin());

std::sort(data.begin(),data.end());

// Now you have sorted data, and the indicies map will map
// your data values to a set of indicies in the original
// vector where that data was found.
// The set in the map allows for data values to appear more
// than once in the original vector.
slurper wrote:

tx for answer Bazarov

i have another problem

i have a vector with 20 elements in it (20 ints).

i'd like to have the elements sorted in ascending order, but somehow i need
to know what index the element was at in the original vector.

someone?
tx for quick and good answers so far