Get Disjunctive Support for itemset?

Question

Disjunctive Support :
let an itemset I formed by any non-empty subset from C
Supp(I) is the number of transactions containing at least one item of I for example i have :

vector < vector <int> > transactions = {{1, 2},
                                        {2, 3, 7},
                                        {4,6},
                                        {1,5,8}};
vector<int> I ={1,2};

expected result : Supp(I) = 3
but my code return Supp(I) = 1

#include <iostream>
#include <vector>
using namespace std;
int getSupport(vector < vector<int> > &transactions, vector<int> item) {
        int ret = 0;
        for(auto&row:transactions){
            int i, j;
            if(row.size() < item.size()) continue;
            for(i=0, j=0; i < row.size();i++) {
                if(j==item.size()) break;
                if(row[i] == item[j]) j++;
            }
            if(j==item.size()){
                ret++;
            }
        }
        return ret;
    }
int main() {
     vector < vector <int> > transactions = {{1, 2},
                                           {2, 3, 7},
                                           {4,6},
                                           {1,5,8}};
     vector <int> I={1,2};
 
     int D = getSupport(transactions, I);
     printf("Disjunctive support = %d",D);
   
    return 0;
}

Answer 1

You wrote that:

Supp(I) is the number of transactions containing at least one item of I

But your implementation looks like you are trying to count transactions containing all the items of I.

Anyway if you still need implementation for the defintion you supplied, you can try this:

#include <iostream>
#include <vector>

int getSupport(std::vector<std::vector<int>> const & transactions, std::vector<int> const & item) {
    int ret = 0;
    for (auto const & tran : transactions) {
        bool bFoundAtLeastOne{ false };
        for (auto const & tran_elem : tran) {
            for (auto const & item_elem : item)
            {
                if (tran_elem == item_elem)
                {
                    ret++;
                    bFoundAtLeastOne = true;
                    break;
                }
            }
            if (bFoundAtLeastOne) {
                break;
            }
        }
    }
    return ret;
}

int main() {
    std::vector<std::vector<int>> transactions = 
        { { 1, 2 },
          { 2, 3, 7 },
          { 4,6 },
          { 1,5,8 } };
    std::vector<int> I = { 1,2 };
    int D = getSupport(transactions, I);
    printf("Disjunctive support = %d\n", D);
    return 0;
}

Some notes:

1. Better to avoid using namespace std - see here Why is "using namespace std;" considered bad practice?
2. I changed passing all the vectors by const& for efficiency and safety.