vector of pointers to a vector of objects, pointer or iterator?

[2kaud]

It looks like this needs something like a double de-reference to access the original object values, (*subset_row)->c_distance. Is that correct?

In the loop it is an iterator so needs a de-reference to get the value - which is an iterator which needs a deference to get the actual data.

Am I right that you can't just use (*data_subset[i]) as if it were an iterator?

data_subset[i] is an iterator - so *(data_subset[i]) gives the underlying data. However, you'd normally use -> as

	for (size_t e = 0; e < data_subset.size(); ++e)
		cout << data_subset[e]->row_name << " " << data_subset[e]->c_distance << endl;

Maybe something like,

or maybe

#include <vector>
#include <string>
#include <algorithm>
#include <iostream>

using namespace std;

class row_data {
public:

	// class constructor
	row_data() : set_A(false), set_B(false), id(0), c_distance(0.0), row_name("") { }

	// member variables
	bool set_A, set_B;
	unsigned int id;
	double c_distance;
	std::string row_name;
	std::vector<double> double_data;
};

typedef std::vector<row_data>::const_iterator row_data_vec_it;
typedef std::vector<row_data_vec_it>::const_iterator veccit;

bool sort_vec_it_sm2lg_c_distance(row_data_vec_it a, row_data_vec_it b) { return a->c_distance < b->c_distance; }

int main()
{
	vector<row_data> data_rows;

	// populate data_rows

	// data subset container
	vector<row_data_vec_it> data_subset;

	for (row_data_vec_it location = data_rows.begin(); location != data_rows.end(); ++location)
		if (location->set_B) { data_subset.push_back(location); }

	// after data_subset has been populated, sort on c_distance
	sort(data_subset.begin(), data_subset.end(), sort_vec_it_sm2lg_c_distance);

	// now we have a sorted subset of the original data
	for (veccit point_B = data_subset.begin(); point_B != data_subset.end() - 2; ++point_B)
		for (veccit point_A = point_B + 1; point_A < data_subset.end() - 1; ++point_A)
			for (veccit point_D = point_A + 1; point_D < data_subset.end(); ++point_D) {

				// print some stuff
				cout << "current set of three points is" << endl;
				cout << "point_B: " << (*point_B)->row_name << endl;
				cout << "point_A: " << (*point_A)->row_name << endl;
				cout << "point_D: " << (*point_D)->row_name << endl;

				// pass to a function
			}
}

[2kaud]

you have declared a second kind if iterator to iterate over the vector of iterators

If you moved from c++98 to the latest c++17 standard, you wouldn't need to define iterator types at all! Consider

#include <vector>
#include <string>
#include <algorithm>
#include <iostream>

using namespace std;

class row_data {
public:
	bool set_A = false, set_B = false;
	unsigned int id = 0;
	double c_distance = 0.0;
	std::string row_name;
	std::vector<double> double_data;
};

int main()
{
	vector<row_data> data_rows;

	// populate data_rows

	// data subset container
	vector<decltype(data_rows.cbegin())> data_subset;

	for (auto location = data_rows.cbegin(); location != data_rows.cend(); ++location)
		if (location->set_B)
			data_subset.push_back(location);

	// after data_subset has been populated, sort on c_distance
	sort(data_subset.begin(), data_subset.end(), [](const auto& a, const auto& b) {return a->c_distance < b->c_distance;});

	// now we have a sorted subset of the original data
	for (auto point_B = data_subset.cbegin(); point_B < data_subset.cend() - 2; ++point_B)
		for (auto point_A = point_B + 1; point_A < data_subset.cend() - 1; ++point_A)
			for (auto point_D = point_A + 1; point_D < data_subset.cend(); ++point_D) {

				// print some stuff
				cout << "current set of three points is" << endl;
				cout << "point_B: " << (*point_B)->row_name << endl;
				cout << "point_A: " << (*point_A)->row_name << endl;
				cout << "point_D: " << (*point_D)->row_name << endl;

				// pass to a function
			}
}

The only 'explicit' type that is used is vector<row_data>!

[abhishek_sachdeva]

I have same issue but still can't resolve. If you found any best solution please let me know.