Removing elements from vector

[kaferro]

I cannot relieve that I am working on Thanksgiving, but I am stuck over
something that should be simple. I have a vector that has twenty-four
elements. I need to remove the four elements whose positions equal
zero. The code below only removes two of the four. Any ideas?

logfile << "\n\n\n. . .removing flat positions";
logfile << "vector size=" << componentPerfor mance.size() << endl;
int position=0;
for (vector<cPerfor mance>::iterato r itr =
componentPerfor mance.begin();i tr!=componentPe rformance.end() ; ++itr)
{
position=itr->returnPosition (); //returnPosition( ) returns a float
logfile << endl << itr->returnSymbol () << "Position=" <<
itr->returnPosition ();
if(position==0)
{
logfile << "\tremoving . . . " << itr->returnSymbol() ;
componentPerfor mance.erase(itr );
}
}

logfile.close() ;

[dasjotre]

Use typedefs!

if cPerformance is cheep to copy:

typedef ::std::vector<c Performance container_t;
container_t tmp;
::std::remove_c opy_if(componen tPerformance.be gin(),component Performance.end (),
::std::back_ins erter(tmp),
!::boost::bind( ::std::not_equa l_to<int>(),
::boost::bind(& cPerformance:: returnPosition, _1), 0));

componentPerfor mance.swap(tmp) ;

if it is not cheap to copy don't
keep them in a vector,

say container_t is a list
typedef ::std::list<cPe rformance container_t;

your loop would look something like:

for(container_t ::iterator it = componentPerfor mance.begin();
it != componentPerfor mance.end(); ++it)
{
if((*it). returnPosition( ) == 0)
it = componentPerfor mance.erase(it) ;
}

[Mirek Fidler]

ka*****@hotmail .com wrote:

I cannot relieve that I am working on Thanksgiving, but I am stuck over
something that should be simple. I have a vector that has twenty-four
elements. I need to remove the four elements whose positions equal
zero. The code below only removes two of the four. Any ideas?

logfile << "\n\n\n. . .removing flat positions";
logfile << "vector size=" << componentPerfor mance.size() << endl;
int position=0;
for (vector<cPerfor mance>::iterato r itr =
componentPerfor mance.begin();i tr!=componentPe rformance.end() ; ++itr)
{
position=itr->returnPosition (); //returnPosition( ) returns a float
logfile << endl << itr->returnSymbol () << "Position=" <<
itr->returnPosition ();
if(position==0)
{
logfile << "\tremoving . . . " << itr->returnSymbol() ;
componentPerfor mance.erase(itr );
}
}

logfile.close() ;

Classic error :-)

When you "erase" the element, 'itr' in fact points already to next one
(technically, in fact it is invalidated by standard AFAIK). Therefore
++itr at the end of "for" skips the element next to the removed one.

Mirek

[Mirek Fidler]

dasjotre wrote:

Use typedefs!

if cPerformance is cheep to copy:

typedef ::std::vector<c Performance container_t;
container_t tmp;
::std::remove_c opy_if(componen tPerformance.be gin(),component Performance.end (),
::std::back_ins erter(tmp),
!::boost::bind( ::std::not_equa l_to<int>(),
::boost::bind(& cPerformance:: returnPosition, _1), 0));

componentPerfor mance.swap(tmp) ;

No wonder nobody outside C++ ghetto considers C++ to be language
suitable to do any real work anymore :)

for(container_t ::iterator it = componentPerfor mance.begin();
it != componentPerfor mance.end(); ++it)
{
if((*it). returnPosition( ) == 0)
it = componentPerfor mance.erase(it) ;
}

I believe this code is wrong - it skips elements past removed one.

[dasjotre]

Mirek Fidler wrote:

dasjotre wrote:

Use typedefs!

if cPerformance is cheep to copy:

typedef ::std::vector<c Performance container_t;
container_t tmp;
::std::remove_c opy_if(componen tPerformance.be gin(),component Performance.end (),
::std::back_ins erter(tmp),
!::boost::bind( ::std::not_equa l_to<int>(),
::boost::bind(& cPerformance:: returnPosition, _1), 0));

componentPerfor mance.swap(tmp) ;

No wonder nobody outside C++ ghetto considers C++ to be language
suitable to do any real work anymore :)

A call for a simpler example !

inline bool operator == (cPerformance const & l, cPerformance const &
r)
{
return l.returnPositio n() == r.returnPositio n();
}

cPerformance nulperf(0);

::std::remove_c opy(componentPe rformance.begin (),componentPer formance.end(),
::std::back_ins erter(tmp), nulperf);
componentPerfor mance.swap(tmp) ;

Which one would teach you more?

for(container_t ::iterator it = componentPerfor mance.begin();
it != componentPerfor mance.end(); ++it)
{
if((*it). returnPosition( ) == 0)

{

it = componentPerfor mance.erase(it) ;

continue;
}

}

I believe this code is wrong - it skips elements past removed one.

Not any more ;)

[dasjotre]

dasjotre wrote:

Mirek Fidler wrote:

dasjotre wrote:

Use typedefs!
>
if cPerformance is cheep to copy:
>
typedef ::std::vector<c Performance container_t;
container_t tmp;
::std::remove_c opy_if(componen tPerformance.be gin(),component Performance.end (),
::std::back_ins erter(tmp),
!::boost::bind( ::std::not_equa l_to<int>(),
::boost::bind(& cPerformance:: returnPosition, _1), 0));
>
componentPerfor mance.swap(tmp) ;

No wonder nobody outside C++ ghetto considers C++ to be language
suitable to do any real work anymore :)

A call for a simpler example !

inline bool operator == (cPerformance const & l, cPerformance const &
r)
{
return l.returnPositio n() == r.returnPositio n();
}

cPerformance nulperf(0);

::std::remove_c opy(componentPe rformance.begin (),componentPer formance.end(),
::std::back_ins erter(tmp), nulperf);
componentPerfor mance.swap(tmp) ;

Which one would teach you more?

for(container_t ::iterator it = componentPerfor mance.begin();
it != componentPerfor mance.end(); ++it)
{
if((*it). returnPosition( ) == 0)

{

it = componentPerfor mance.erase(it) ;

continue;
}

}

I believe this code is wrong - it skips elements past removed one.

Not any more ;)

My humblest appologies.

container_t::it erator it = componentPerfor mance.begin();
while(it != componentPerfor mance.end())
{
if((*it).return Position() == 0)
it = componentPerfor mance.erase(it) ;
else
++it;
}

Good example to argue against hand coded loops

[Mirek Fidler]

container_t::it erator it = componentPerfor mance.begin();
while(it != componentPerfor mance.end())
{
if((*it).return Position() == 0)
it = componentPerfor mance.erase(it) ;
else
++it;
}

Good example to argue against hand coded loops

Good example to teach you check twice before hitting Post button ;)

Do not worry, happens to me all the time.

Mirek

[dasjotre]

Mirek Fidler wrote:

container_t::it erator it = componentPerfor mance.begin();
while(it != componentPerfor mance.end())
{
if((*it).return Position() == 0)
it = componentPerfor mance.erase(it) ;
else
++it;
}

Good example to argue against hand coded loops

Good example to teach you check twice before hitting Post button ;)

I know, I'm a trigger happy poster :o)

[loic-dev]

ka*****@hotmail .com schrieb:

I cannot relieve that I am working on Thanksgiving, but I am stuck over
something that should be simple. I have a vector that has twenty-four
elements. I need to remove the four elements whose positions equal
zero. The code below only removes two of the four. Any ideas?

The componentPerfor mance.erase() update the iterator to the next
element. Hence, if you still want to use your for(...) loop, you have
to change the if statement as follows:

if(position==0)
{
logfile << "\tremoving . . . " << itr->returnSymbol() ;
componentPerfor mance.erase(itr );
--itr; // because itr points to the next element.
}

HTH,
Loic.

[Salt_Peter]

ka*****@hotmail .com wrote:

I cannot relieve that I am working on Thanksgiving, but I am stuck over
something that should be simple. I have a vector that has twenty-four
elements. I need to remove the four elements whose positions equal
zero. The code below only removes two of the four. Any ideas?

logfile << "\n\n\n. . .removing flat positions";
logfile << "vector size=" << componentPerfor mance.size() << endl;
int position=0;
for (vector<cPerfor mance>::iterato r itr =
componentPerfor mance.begin();i tr!=componentPe rformance.end() ; ++itr)
{
position=itr->returnPosition (); //returnPosition( ) returns a float
logfile << endl << itr->returnSymbol () << "Position=" <<
itr->returnPosition ();
if(position==0)
{
logfile << "\tremoving . . . " << itr->returnSymbol() ;
componentPerfor mance.erase(itr );
}
}

logfile.close() ;

template the functor...

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

struct VerifyPos0
{
bool operator()(cons t cPerformance& r_x)
{
// a float??
return 0 == static_cast<int >(r_x.returnPos ition());
}
};

int main()
{
std::vector< cPerformance componentPerfor mance;
...

componentPerfor mance.erase(
std::remove_if( componentPerfor mance.begin(),
componentPerfor mance.end(),
VerifyPos0()),
componentPerfor mance.end() );
...
}