Iterator for 2D Vector

iterator for 2d vector

Although your question is not very clear, I'm going to assume you mean a 2D vector to mean a vector of vectors:

vector< vector<int> > vvi;

Then you need to use two iterators to traverse it, the first the iterator of the "rows", the second the iterators of the "columns" in that "row":

//assuming you have a "2D" vector vvi (vector of vector of int's)
vector< vector<int> >::iterator row;
vector<int>::iterator col;
for (row = vvi.begin(); row != vvi.end(); row++) {
    for (col = row->begin(); col != row->end(); col++) {
        // do stuff ...
    }
}

Iteration in 2D Vector in C++

You can iterate like this,

int main()
{
    vector< vector<int>> vec;
    for(int i=0;i<vec.size();i++)
    {
        for(int j=0;j<vec[i].size();j++)
           cout<<vec[i][j]<<" ";
        cout<<endl;
    }
}

C++: vectorvectorint iterator?

I am wondering if i is an iterator of an entire 1D array?

Well, vec2d is a vector of vector<int> and i is vec2d's iterator. You can consider vec2d a 1d vector of 1d vector, and if so, i is an iterator for the entire vec2d (which is, as mentioned, a 1-d vector), or you can look at it as a 2d vector of ints (which I see as less trivial option).

Notice that not all 1d vectors are the same. Even if you consider vec2d as a 1d vector, its a vector OF vector<int>, hence something like this little shenanigan i = tmp2.begin(); (from my example below) will not compile.

Basically an iterator can iterate on a specific container type, be it a vector of ints, or vector of vectors of whatever. The distinction between 1d and 2d vectors isn't the issue, as I see it.

what is that (*i) [1] mean?

Consider the following:

#include <iostream>
#include <vector>
using namespace std;

int main(){

    vector< vector<int> > vec2d;

    vector<int> tmp1;
    tmp1.push_back(1);
    tmp1.push_back(2);

    vector<int> tmp2;
    tmp2.push_back(3);
    tmp2.push_back(4);

    vec2d.push_back(tmp1);
    vec2d.push_back(tmp2);

    vector< vector<int> >::iterator i, iEnd;
    i = vec2d.begin();
    iEnd = vec2d.end();

    cout << (*i)[1] << endl;        // outputs 2 (same as vec2d[0][1])
    cout << vec2d[0][1] << endl;    // outputs 2
    cout << vec2d[1][0] << endl;    // outputs 3
    cout << vec2d[1][1] << endl;    // outputs 4

    return 0;
}

As you can see, *i takes you "inside" the container you iterate over (in your case, vec2d) and the [1] gives you the 2nd element of that inner-container.

Notice that *i[0] != (*i)[0] because of operator-precedence (in my example case it doesn't even compile).

How do I iterate through a two dimensional vector

Or since we're using c++11...

#include <iostream>
#include <vector>

using namespace std;

int main() {

  vector<vector<int> > v = {{1,2}, {3,4}};
  for (const auto& inner : v) {
      for (const auto& item : inner) {
          cout << item << " ";
      }
  }
  cout << endl;

  return 0;
}

How can I iterate over a 2D vector in functional style?

Use flatten:

fn main() {
    let v = vec![vec![1, 2], vec![3, 4], vec![5, 6]];

    for i in v.iter().flatten() {
        println!("{}", i); // 1 2 3 4 5 6
    }
}

flatten transforms nested iterators into one iterator.

---

Related Topics