Re: remove_if with a mask

eLVa <>
Tue, 8 Jun 2010 08:43:55 -0700 (PDT)
On 8 juin, 11:36, Victor Bazarov <v.baza...@comcast.invalid> wrote:

On 6/8/2010 11:18 AM, Paul Bibbings wrote:

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


    template<typename T>
    class MaskFunctor {
       explicit MaskFunctor(std::vector<bool>& mask)
          : mask_(mask)
          , mask_iter_(mask_.begin())
       { }
       bool operator()(const T&)
          if (mask_iter_ == mask_.end())
            return false;
            return *mask_iter_++;
       std::vector<bool>& mask_;
       std::vector<bool>::const_iterator mask_iter_;

    int main()
       std::vector<bool> mask;
       for (int i = 0; i< 4; ++i)

       std::vector<int> i_vec;
       for (int i = 0; i< 8; ++i)

       std::vector<int>::iterator end =
          std::remove_if(i_vec.begin(), i_vec.end(), MaskFunc=


       i_vec.erase(end, i_vec.end());

       for (std::vector<int>::const_iterator ci = i_vec.begin=


              ci != i_vec.end();
          std::cout<< *ci<< ' ';
       std::cout<< '\n';

    16:15:41 Paul Bibbings@JIJOU
    /cygdrive/d/CPPProjects/CLCPP $./vector_mask
    2 4 6

The implementation makes a copy of the predicate. It's important that
the predicate keeps the iterator by reference. Try rewriting it with
that in mind.

I tried :

template <class Z> struct maskChecker {
        maskChecker(const vector<bool> &mask) : it(mask.begin()) {}
        bool operator()(Z &) const { return *it ++; }
        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(),
    typename vector<Z>::iterator end = remove_if(data.begin(),
data.end(), maskChecker<Z>(mask));
    data.erase(end, data.end());

This does not compile ...
I know this is about it being initialized by a temporary variable
returned by mask.begin() ..
Should I directly pass a reference to the iterator to the constructor
of maskChecker rather than the vector itself ?

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