Thread: partition a vector of vectors

  1. #1
    Registered User
    Join Date
    Jun 2006

    partition a vector of vectors


    I am working in this problem, where I have a set of N d-dimensional points, e.g. (4,5,6,8) (2,0,4,6), are 4-d points, which I have stored in a vector of vectors.

    I am trying to partition the vector of vectors according to the median value of one the dimensions.

    I tried to use the stl partition method like this:
    // S is a vector of vectors containing the points
    vector < vector <int> >::iterator iter;
    vector < vector <int> >::iterator pos_beg = S.begin();
    vector < vector <int> >::iterator pos_end = S.end();
    iter = partition (pos_beg, pos_end, bind2nd( is_less(d),median)  );
    // "is_less" is a class I use to sort the vector of vectors according to an arbitraty dimension.
    // e.g. sort(S.begin(), S.end(), is_less(d));
    class is_less  {
        is_less(const int index = 0): i(index) {}
        bool operator()(const vector<int>& v1, const vector<int>& v2) {
            return v1[i] < v2[i];
        const int i;
    Unfortunately, it doesn't work, (or compile correctly). It seems that I have a problem with the predicate of the partition method; the bind2nd function I saw it in an example, but it worked there for just a common vector, and does not seem to work in this case.

    Would anyone know how I might solve this problem with the partition.

    Last edited by acosgaya; 10-06-2006 at 11:24 AM.

  2. #2
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    I believe your operator() should be const.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

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