title: push_back problem on vector<vector<int> >
body: <p>Dear All,<br>
  I used a vector of vector, say <code>vector&lt;vector&lt;int&gt; &gt; no_1_2</code> to store elements of two <code>vector&lt;int&gt;</code> containers, say no1 &amp; no2. so for e.g. i would say, no1={2,5,7,10,3} and no2={21,34,15}.  </p>
  
  <p>I wanted to store these 2 vectors in one container called no_1_2 and I used <code>no_1_2[0].push_back(no1.at(i))</code> and <code>no_1_2[1].push_back(no2.at(j))</code> within two 'for' loops. But, i got error. is there anyway to solve this?  </p>
  
  <p>Can't i push_back vector of vector? any help please..
  thanks</p>
  
  <p>sorry here is part of my code,
  //some classes and some codes are here</p>
  
  <pre><code>vector&lt; vector&lt;int&gt; &gt; final_list(int code1,int code2){
     vector&lt;vector&lt;int&gt; &gt; no_1_2;
     vector&lt;int&gt; in;
     vector&lt;int&gt; out;
     for (int foo=0;foo&lt;size();foo++){
         int a_point=foo;
         if (at(a_point).Code()==code1){
             vector&lt;int&gt; closer_points;
             closer_points=at(foo).Closers();
             for (int fee=0;fee&lt;closer_points.size();fee++){
                 int a_neb_point=closer_points.at(fee);
                 if (at(a_neb_point).Code()==code2){
                      in.push_back(a_point);  
                      out.push_back(a_neb_point);  
                      }
                 }
             }
         }
     /remove duplicates // above in and out vectors containing some values repeatedly, so, i remove the duplicates here
     for(vector&lt;int&gt;::iterator i=in.begin();i!=in.end();i++){
       sort(in.begin(),in.end());
       in.erase(unique(in.begin(),in.end()),in.end()); 
       no_1_2[0].push_back(*i);
       }
     for(vector&lt;int&gt;::iterator o=out.begin();o!=out.end();o++){
       sort(out.begin(),out.end());
       out.erase(unique(out.begin(),out.end()),out.end());
       no_1_2[1].push_back(*o);
       }
     return no_1_2;
     }
  
  int main (){
  // some code
  
  vector&lt; vector &lt;int&gt; &gt; in_out=mylist.final_list(34,1); //here i just tried for code    values for (34, 1), like that i have many sets
  }
  </code></pre>