copy from keys from multimap into the vector

[puzzlecracker]

I am using while loop for that but I am sure you can do it quicker and
more syntactically clear with copy function.

Here is what I do and would like to if someone has a cleaner solution:

vector<stringve c;
multimap<stirng , intmyMap

// populate myMap

multimap<string , int >::iterator iter = myMap.begin();

while(iter != myMap.end())
{
vec.push_back(i ter->first)
}

[peter koch]

Re: copy from keys from multimap into the vector

On 29 Okt., 20:33, puzzlecracker <ironsel2...@gm ail.comwrote:

I am using while loop for that but I am sure you can do it quicker and
more syntactically clear with copy function.
>
Here is what I do and would like to if someone has a cleaner solution:
>
    vector<stringve c;
    multimap<stirng , intmyMap
>
   // populate myMap
>
    multimap<string , int >::iterator iter = myMap.begin();
>
    while(iter != myMap.end())
    {
           vec.push_back(i ter->first)
    }

Whats wrong with
std::copy(myMap .begin(),myMap. end(),std::back _inserter(vec)) ; ?

You could do a reserve on vec first to improve performance.

/Peter

[AnonMail2005@gmail.com]

Re: copy from keys from multimap into the vector

I am using while loop for that but I am sure you can do it quicker and

more syntactically clear with copy function.

>

Here is what I do and would like to if someone has a cleaner solution:

>

    vector<stringve c;
    multimap<stirng , intmyMap

>

   // populate myMap

>

    multimap<string , int >::iterator iter = myMap.begin();

>

    while(iter != myMap.end())
    {
           vec.push_back(i ter->first)
    }

>
Whats wrong with
std::copy(myMap .begin(),myMap. end(),std::back _inserter(vec)) ; ?
>

A map's element contains both the key and the value so this is not
correct.
The OP just wants the key.

[Obnoxious User]

Re: copy from keys from multimap into the vector

On Wed, 29 Oct 2008 12:33:38 -0700, puzzlecracker wrote:

I am using while loop for that but I am sure you can do it quicker and
more syntactically clear with copy function.
>
Here is what I do and would like to if someone has a cleaner solution:
>
vector<stringve c;
multimap<stirng , intmyMap
>
// populate myMap
>
multimap<string , int >::iterator iter = myMap.begin();
>
while(iter != myMap.end())
{
vec.push_back(i ter->first)
}

#include <vector>
#include <map>
#include <iterator>
#include <algorithm>
#include <iostream>

template<typena me C, typename M>
class key_inserter :
public std::iterator<s td::output_iter ator_tag,void,v oid,void,void{
private:
C & d_coll;
public:
key_inserter(C & c) : d_coll(c) {}
key_inserter & operator*() { return *this; }
key_inserter & operator++() { return *this; }
key_inserter & operator++(int) { return *this; }
key_inserter &
operator=(typen ame M::value_type const & p) {
d_coll.push_bac k(p.first);
return *this;
}
};

template<typena me C, typename M>
key_inserter<C, Mmake_key_inser ter(C & c, M & m) {
return key_inserter<C, M>(c);
}

int main() {
std::vector<int v;
std::map<int,in tm;
m[0];m[1];m[2];m[6];
std::copy(m.beg in(),
m.end(),
make_key_insert er(v,m));
std::copy(v.beg in(),
v.end(),
std::ostream_it erator<int>(std ::cout,"\n"));
return 0;
}

--
OU
Remember 18th of June 2008, Democracy died that afternoon.

http://frapedia.se/wiki/Information_in_English

[peter koch]

Re: copy from keys from multimap into the vector

On 29 Okt., 22:25, "AnonMail2...@g mail.com" <AnonMail2...@g mail.com>
wrote:

I am using while loop for that but I am sure you can do it quicker and
more syntactically clear with copy function.

>

Here is what I do and would like to if someone has a cleaner solution:

>

    vector<stringve c;
    multimap<stirng , intmyMap

>

   // populate myMap

>

    multimap<string , int >::iterator iter = myMap.begin();

>

    while(iter != myMap.end())
    {
           vec.push_back(i ter->first)
    }

>

Whats wrong with
std::copy(myMap .begin(),myMap. end(),std::back _inserter(vec)) ; ?

>
A map's element contains both the key and the value so this is not
correct.
The OP just wants the key.

I did not see that. Don't ask the question in the title (but read the
title anyway!).
In that case, I'd recommend having a look at Boosts iterator adaptors
which should do the job. But I admit that I haven't looked at that
part of Boost for a while (and never used it).

/Peter

[AnonMail2005@gmail.com]

Re: copy from keys from multimap into the vector

I am using while loop for that but I am sure you can do it quicker and

more syntactically clear with copy function.
>
Here is what I do and would like to if someone has a cleaner solution:
>
    vector<stringve c;
    multimap<stirng , intmyMap
>
   // populate myMap
>
    multimap<string , int >::iterator iter = myMap.begin();
>
    while(iter != myMap.end())
    {
           vec.push_back(i ter->first)
    }

I think this works:

struct MyFunctor
{
typedef std::multimap <std::string, intStringIntMul tiMap;

std::string operator () (StringIntMulti Map::value_type const & v)
const
{
return v.first;
}
};

std::transform (myMap.begin (), myMap.end (), back_inserter (vec),
MyFunctor ());

HTH

[Salt_Peter]

Re: copy from keys from multimap into the vector

On Oct 29, 2:33 pm, puzzlecracker <ironsel2...@gm ail.comwrote:

I am using while loop for that but I am sure you can do it quicker and
more syntactically clear with copy function.
>
Here is what I do and would like to if someone has a cleaner solution:
>
    vector<stringve c;
    multimap<stirng , intmyMap
>
   // populate myMap
>
    multimap<string , int >::iterator iter = myMap.begin();
>
    while(iter != myMap.end())
    {
           vec.push_back(i ter->first)
    }

You'll need a functor to extract that string from multimap's
value_type and std::transform can process the elements.

#include <iostream>
#include <ostream>
#include <string>
#include <vector>
#include <map>
#include <iterator>

template< typename P >
struct extract_first
{
const typename P::first_type&
operator()(cons t P& p) const
{
return p.first;
}
};

int main()
{
std::vector< std::string vec;
std::multimap< std::string, int mm;

// populate mm

typedef std::multimap< std::string, int >::value_type VType;

std::transform( mm.begin(),
mm.end(),
std::back_inser ter(vec),
extract_first< VType >() );
}

[puzzlecracker]

Re: copy from keys from multimap into the vector

On Oct 29, 5:25 pm, "AnonMail2...@g mail.com" <AnonMail2...@g mail.com>
wrote:

I am using while loop for that but I am sure you can do it quicker and
more syntactically clear with copy function.

>

Here is what I do and would like to if someone has a cleaner solution:

>

    vector<stringve c;
    multimap<stirng , intmyMap

>

   // populate myMap

>

    multimap<string , int >::iterator iter = myMap.begin();

>

    while(iter != myMap.end())
    {
           vec.push_back(i ter->first)
    }

>

Whats wrong with
std::copy(myMap .begin(),myMap. end(),std::back _inserter(vec)) ; ?

>
A map's element contains both the key and the value so this is not
correct.
The OP just wants the key.

Exactly... that's not going to work, I don't need the value_key, which
is pair<string, int>

Thanks

[Juha Nieminen]

Re: copy from keys from multimap into the vector

Obnoxious User wrote:

#include <vector>
#include <map>
#include <iterator>
#include <algorithm>
#include <iostream>
>
template<typena me C, typename M>
class key_inserter :
public std::iterator<s td::output_iter ator_tag,void,v oid,void,void{
private:
C & d_coll;
public:
key_inserter(C & c) : d_coll(c) {}
key_inserter & operator*() { return *this; }
key_inserter & operator++() { return *this; }
key_inserter & operator++(int) { return *this; }
key_inserter &
operator=(typen ame M::value_type const & p) {
d_coll.push_bac k(p.first);
return *this;
}
};
>
template<typena me C, typename M>
key_inserter<C, Mmake_key_inser ter(C & c, M & m) {
return key_inserter<C, M>(c);
}
>
int main() {
std::vector<int v;
std::map<int,in tm;
m[0];m[1];m[2];m[6];
std::copy(m.beg in(),
m.end(),
make_key_insert er(v,m));
std::copy(v.beg in(),
v.end(),
std::ostream_it erator<int>(std ::cout,"\n"));
return 0;
}

Given that the while loop solution only requires 2 lines of code, I
think it's the easier solution... ;)

[Salt_Peter]

Re: copy from keys from multimap into the vector

On Oct 29, 2:33 pm, puzzlecracker <ironsel2...@gm ail.comwrote:

I am using while loop for that but I am sure you can do it quicker and
more syntactically clear with copy function.
>
Here is what I do and would like to if someone has a cleaner solution:
>
    vector<stringve c;
    multimap<stirng , intmyMap
>
   // populate myMap
>
    multimap<string , int >::iterator iter = myMap.begin();
>
    while(iter != myMap.end())
    {
           vec.push_back(i ter->first)
    }

You could use std::transform with std::back_inser ter to load vector
and a functor to extract the std::string from multimap's value_type.

#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iterator>

template< typename P >
struct extract_first
{
const typename P::first_type&
operator()(cons t P& p) const
{
return p.first;
}
};

int main()
{
std::vector< std::string vec;
std::multimap< std::string, int mm;
// populate mm

typedef std::multimap< std::string, int >::value_type VType;

std::transform( mm.begin(),
mm.end(),
std::back_inser ter(vec),
extract_first< VType >() );
}

[Kai-Uwe Bux]

Re: copy from keys from multimap into the vector

Salt_Peter wrote:

On Oct 29, 2:33 pm, puzzlecracker <ironsel2...@gm ail.comwrote:

>I am using while loop for that but I am sure you can do it quicker and
>more syntactically clear with copy function.
>>
>Here is what I do and would like to if someone has a cleaner solution:
>>
>vector<stringv ec;
>multimap<stirn g, intmyMap
>>
>// populate myMap
>>
>multimap<strin g, int >::iterator iter = myMap.begin();
>>
>while(iter != myMap.end())
>{
>vec.push_back( iter->first)
>}

>
You could use std::transform with std::back_inser ter to load vector
and a functor to extract the std::string from multimap's value_type.
>
#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iterator>
>
template< typename P >
struct extract_first
{
const typename P::first_type&
operator()(cons t P& p) const
{
return p.first;
}
};
>
int main()
{
std::vector< std::string vec;
std::multimap< std::string, int mm;
// populate mm
>
typedef std::multimap< std::string, int >::value_type VType;
>
std::transform( mm.begin(),
mm.end(),
std::back_inser ter(vec),
extract_first< VType >() );
}

Alternatively, one can put the template inside:

// same headers

struct extract_first {

template< typename P >
typename P::first_type const &
operator()(cons t P& p) const {
return p.first;
}

};

int main() {
std::vector< std::string vec;
std::multimap< std::string, int mm;
// populate mm

std::transform( mm.begin(),
mm.end(),
std::back_inser ter(vec),
extract_first() );
}

This makes extract_first oblivious to the type actually being used. I am not
sure, which is better. Any thoughts?


Best

Kai-Uwe Bux

[Triple-DES]

Re: copy from keys from multimap into the vector

On 30 Okt, 01:40, Kai-Uwe Bux <jkherci...@gmx .netwrote:

Salt_Peter wrote:

You could use std::transform with std::back_inser ter to load vector
and a functor to extract the std::string from multimap's value_type.

>

#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <iterator>

>

template< typename P >
struct extract_first
{
  const typename P::first_type&
  operator()(cons t P& p) const
  {
    return p.first;
  }
};

>

int main()
{
  std::vector< std::string vec;
  std::multimap< std::string, int mm;
  // populate mm

>

  typedef std::multimap< std::string, int >::value_type VType;

>

  std::transform( mm.begin(),
                  mm.end(),
                  std::back_inser ter(vec),
                  extract_first< VType >() );
}

>
Alternatively, one can put the template inside:
>
// same headers
>
struct extract_first {
>
  template< typename P >
  typename P::first_type const &
  operator()(cons t P& p) const {
    return p.first;
  }
>
};
>
int main() {
  std::vector< std::string vec;
  std::multimap< std::string, int mm;
  // populate mm
>
  std::transform( mm.begin(),
                  mm.end(),
                  std::back_inser ter(vec),
                  extract_first() );
>
}
>
This makes extract_first oblivious to the type actually being used. I am not
sure, which is better. Any thoughts?
>

I like your solution, but the "canonical" solution, I think, is the
former (looking at SGI's select1st functor). That being said, I can't
think of a case where your solution would be any worse.

[SG]

Re: copy from keys from multimap into the vector

On 30 Okt., 03:40, puzzlecracker <ironsel2...@gm ail.comwrote:

Given that the while loop solution only requires 2 lines of code, I
think it's the easier solution... ;)

>
That's exactly my point. Guys, do you see how this solution is
verbose, cluttered, and not particularly expressive over my
traditional solution?

Well, the "extract_fi rst" functor is reusable. You only have to write
it down once. Your problem is solved with one function call. Also, I
like the fact that Kai-Uwe's solution is NOT cluttered with names of
types (iterator, value_type, ...). In the upcoming C++ version I would
probably prefer the new for-range construct along with type inference
to avoid this:

#include <for>
:
for (auto & p : mymultimap) myvector.push(p .first);
:

This will also avoid the creation of a temporary copy of pair.first
because operator() in extract_first returns a copy. Of course you
could define this function to return a const reference and I think
this will be ok in this situation because the pair reference is NOT a
temporary. But it may lead to danling references in other cases. So,
coding your own loop is more efficient.

Cheers,
SG

[Obnoxious User]

Re: copy from keys from multimap into the vector

On Wed, 29 Oct 2008 23:15:35 +0000, Juha Nieminen wrote:

Obnoxious User wrote:

[snip]

>
Given that the while loop solution only requires 2 lines of code, I
think it's the easier solution... ;)

On the other hand, if this action is required in multiple
places, then I would prefer some sort of abstraction instead
of a simple while loop.

--
OU
Remember 18th of June 2008, Democracy died that afternoon.

http://frapedia.se/wiki/Information_in_English

[James Kanze]

Re: copy from keys from multimap into the vector

On Oct 29, 8:33 pm, puzzlecracker <ironsel2...@gm ail.comwrote:

I am using while loop for that but I am sure you can do it
quicker and more syntactically clear with copy function.

Here is what I do and would like to if someone has a cleaner
solution:

vector<stringve c;
multimap<stirng , intmyMap

// populate myMap

multimap<string , int >::iterator iter = myMap.begin();

while(iter != myMap.end())
{
vec.push_back(i ter->first)
}

Do you really want multiple entries in the vector when there are
multiple entries for a single key in the map? If so, something
like the following should work:

template< typename Pair >
struct First
{
typedef Pair argument_type ;
typedef typename Pair::first_typ e
result_type ;

typename Pair::first_typ e
operator()( Pair const& obj ) const
{
return obj.first ;
}
} ;

and then:

typedef First< Map::value_type >
Mapper ;
typedef boost::transfor m_iterator< Mapper, Map::const_iter ator >
InitIter ;
std::vector< std::string >
k( InitIter( m.begin(), Mapper() ),
InitIter( m.end(), Mapper() ) ) ;

If you only want each unique key to appear once, then you should
be able to use a boost::filter_i terator on the
transform_itera tor.

--
James Kanze (GABI Software) email:james.kan ze@gmail.com
Conseils en informatique orientée objet/
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