Re: remove_if with a mask
eLVa <elvadrias@gmail.com> writes:
On 8 juin, 10:09, "Leigh Johnston" <le...@i42.co.uk> wrote:
"Victor Bazarov" <v.baza...@comcast.invalid> wrote in message
news:hulh6q$46f$1@news.eternal-september.org...
On 6/8/2010 9:13 AM, eLVa wrote:
I have a simple problem : you are given a container, let's say a
vector of some objects, and a vector of bool which is to be treated as
a mask. You have to remove every element from the container for which
the mask is true.
basically, two iterators (one over the container and one over the
mask) iterates through their respective containers, removing elements
from the first when the second is true. I tried a few solutions, using
remove_if but I was not succesful !
Post what you have, post what didn't work, post your explanation on how
you expected it to work. ?Otherwise this looks too much like homework, and
we don't do homework.
Ok ! Wait a minute there, it's not an homework, it's a question I'm
trying to resolve.
I thought that it was not wise to keep an iterator into a functor used
in remove_if. I wanted a direction, that's all.
So that's what I got :
template <class Z> struct maskChecker {
public:
maskChecker(const vector<bool> &mask) : it(mask.begin()) {}
bool operator()(Z &) const { return *it ++; }
private:
mutable vector<bool>::const_iterator it;
};
template <class T> template<class Z>
void Selector<T>::compact(vector<Z> &data, const vector<bool> &mask) {
if (data.size() != mask.size()) throw UnmatchedSize(data.size(),
mask.size());
typename vector<Z>::iterator end = remove_if(data.begin(),
data.end(), maskChecker<Z>(mask));
data.erase(end, data.end());
}
That's kinda working, what's your opinion ?
I threw together something similar to what you have and it *doesn't*
appear to be working.
16:15:35 Paul Bibbings@JIJOU
/cygdrive/d/CPPProjects/CLCPP $cat vector_mask.cpp
// file: vector_mask.cpp
#include <vector>
#include <algorithm>
#include <iostream>
template<typename T>
class MaskFunctor {
public:
explicit MaskFunctor(std::vector<bool>& mask)
: mask_(mask)
, mask_iter_(mask_.begin())
{ }
bool operator()(const T&)
{
if (mask_iter_ == mask_.end())
return false;
else
return *mask_iter_++;
}
private:
std::vector<bool>& mask_;
std::vector<bool>::const_iterator mask_iter_;
};
int main()
{
std::vector<bool> mask;
for (int i = 0; i < 4; ++i)
{
mask.push_back(true);
mask.push_back(false);
}
std::vector<int> i_vec;
for (int i = 0; i < 8; ++i)
i_vec.push_back(i);
std::vector<int>::iterator end =
std::remove_if(i_vec.begin(), i_vec.end(), MaskFunctor<int>(mask));
i_vec.erase(end, i_vec.end());
for (std::vector<int>::const_iterator ci = i_vec.begin();
ci != i_vec.end();
++ci)
{
std::cout << *ci << ' ';
}
std::cout << '\n';
}
16:15:41 Paul Bibbings@JIJOU
/cygdrive/d/CPPProjects/CLCPP $./vector_mask
2 4 6
Regards
Paul Bibbings