How to split vector into subsets? - c++

Question

I'm trying to split the vector into subsets based of the number of process I use in my application. I created the pseudo code but I really don't have any clue how can I output the subsets.
The problem:
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
My code:
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;
}
update
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

i haven't tested this code, but something along the lines of this should work - instead of having your function return one vector, have it return a vector of vectors, like this:
std::vector<std::vector<Residence>> split(std::vector<Residence rs, int num_procs)
this will allow you to split your original vector into num_procs number of vectors, and then push_back() each of those onto your return vector of vectors (kind of like a matrix).
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
}
when you call the function, it will look something like this:
std::vector<std::vector<Residence>> vectors = split(original_vector, 4);
which will allow you to get subvectors like this:
vectors[0]; //first quarter
vectors[1]; //second
vectors[2]; //third
vectors[3]; //fourth + remainder

Answer 2

you need to read one record at time not pass the all subset as vector think you need this
while(!residenceFile.eof())
{
residenceFile >> res.x >>res.y;
if ( numLines % numProcs == rank)
{
//call the process
//populate_distancesVector(res,foodbankData);
analysis_range(populate_distancesVector(res,foodbankData),count);
}
++numLines;
}