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how can i use an iterator for a 2d vector?

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how can i use an iterator for a 2d vector?

Feb 15th, 2007

I have read that iterators are used to traverse through the elements of container classes. If I wanted to use iterators to move through elements of a 2d vector, how am I going to declare it and use it? Maybe what I said was not too clear, let me rephrase it to be : " how can I iterate through a 2d vector?"

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Re: how can i use an iterator for a 2d vector?

Feb 15th, 2007

you mean a vector like below? There are probably other ways too, but this is how I do it.

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
vector< vector< string> > theList;
vector<string>::iterator it;
 
vector<string>& innerList = theList[0];
it = innerList.begin();
for( ; it != innerList.end(); it++)
{
  // blabla
}
vector< vector< string> > theList;
vector<string>::iterator it;

vector<string>& innerList = theList[0];
it = innerList.begin();
for( ; it != innerList.end(); it++)
{
  // blabla
}

Last edited by Ancient Dragon; Feb 15th, 2007 at 12:40 pm.

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Re: how can i use an iterator for a 2d vector?

Feb 15th, 2007

Ancient Dragon's example will work for the first elemend of the 2D vector, and you'll probably have to nest it to go through all the rows of the 2D vector.

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Re: how can i use an iterator for a 2d vector?

Feb 17th, 2007

Do i need to declare another iterator to traverse the rows and another one to traverse each elements? Also, can you show how to do the nesting, since I'm a bit confused?
Thanks.

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Re: how can i use an iterator for a 2d vector?

Feb 17th, 2007

>Do i need to declare another iterator to traverse the rows and another one to traverse each elements?
Yes. Each row is an independent data structure, so you have no choice but to use two iterators. It's exactly the same as when you build the vector of vectors:

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 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <iomanip>
#include <vector>
 
int main()
{
  std::vector< std::vector<int> > v;
 
  for ( int i = 0; i < 10; i++ ) {
    v.push_back ( std::vector<int>() );
 
    for ( int j = 0; j < 10; j++ )
      v[i].push_back ( i + j );
  }
 
  std::vector< std::vector<int> >::iterator row_it = v.begin();
  std::vector< std::vector<int> >::iterator row_end = v.end();
 
  for ( ; row_it != row_end; ++row_it ) {
    std::vector<int>::iterator col_it = row_it->begin();
    std::vector<int>::iterator col_end = row_it->end();
 
    for ( ; col_it != col_end; ++col_it )
      std::cout<< std::setw ( 3 ) << *col_it;
    std::cout<<'\n';
  }
}
#include <iostream>
#include <iomanip>
#include <vector>

int main()
{
  std::vector< std::vector<int> > v;

  for ( int i = 0; i < 10; i++ ) {
    v.push_back ( std::vector<int>() );

    for ( int j = 0; j < 10; j++ )
      v[i].push_back ( i + j );
  }

  std::vector< std::vector<int> >::iterator row_it = v.begin();
  std::vector< std::vector<int> >::iterator row_end = v.end();

  for ( ; row_it != row_end; ++row_it ) {
    std::vector<int>::iterator col_it = row_it->begin();
    std::vector<int>::iterator col_end = row_it->end();

    for ( ; col_it != col_end; ++col_it )
      std::cout<< std::setw ( 3 ) << *col_it;
    std::cout<<'\n';
  }
}