c++ - 如何将 vector 拆分成子集？

Question

我正在尝试根据我在应用程序中使用的进程数将 vector 拆分为子集。我创建了伪代码，但我真的不知道如何输出子集。

问题:

Read a subset of the address records from residences.dat using striping. For n processes, each process evaluates a unique subset of records based on every nth record. The number of records in this subset should be approximately #-of-residence-records /#-of-processes. Across all the parallel processes used no address should be omitted and none should be processed more than once. Also note that only ONE record at a time should be stored in memory by any process

我的代码:

std::vector<Residence> spliteResidenceDaata(vector<Residence> rs,int numProces = 0);
function body 

    std::vector<Residence> spliteResidenceDaata(vector<Residence> rs,int numProces)
    {

        std::vector<Residence> residenceSet;
        //get the size of vector
        int res_set_size = rs.size();
        int sizrOfSubSet =res_set_size/numProces;

        //output the arry subsite some "help here"

        return residenceSet;
    }

更新

I came up with this pseudo code
1-take the number of line in .dat file  rData
2- get the number of data you want to read for each process sizeofLine  (rData.size()/numProc)
3- read the .dat file from line 0 to  sizeofLine
4-output array 

Answer 1

我还没有测试过这段代码，但是与此类似的东西应该可以工作——不是让你的函数返回一个 vector ，而是让它返回一个 vector 的 vector ，就像这样:

std::vector<std::vector<Residence>> split(std::vector<Residence rs, int num_procs)

这将允许您将原始 vector 拆分为 num_procs vector 数，然后是 push_back()每一个都到你的 vector 的返回 vector (有点像矩阵)。

std::vector<std::vector<Residence>> split(const std::vector<Residence> rs, const unsigned num_procs) {
    unsigned j = 0; //position counter
    std::vector<std::vector<Residence>> result; //resulting vector of vectors
    for(unsigned i = 0; i < num_procs; ++i) {   //for each process
        std::vector<Residence> temp;            //create a vector
        for(; j < ((i + 1) * rs.size() / num_procs; ++j)    //iterate
            temp.push_back(rs[j]);              //and populate temporary vector with a 1/num_procs section of original vector
        result.push_back(temp);                 //and push that temporary vector into your result vector of vectors
    }
    for(; j < rs.size(); ++j)                   //finally, if the original vector is not divisible by num_procs
        result[num_procs].push_back(rs[j]);     //push the remainder of elements into the last vector
}

当你调用函数时，它看起来像这样:

std::vector<std::vector<Residence>> vectors = split(original_vector, 4);

这将允许您获得这样的子 vector :

vectors[0];   //first quarter
vectors[1];   //second
vectors[2];   //third
vectors[3];   //fourth + remainder