Deleting columns and rows in 2D vector

[asput]

Hello,

I am struggling to delete one column and one row from a 2D vector, where the column and row to be deleted depend on the position of the element, not its contents.

Without using an iterator I can delete a row, but not a column:

#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

int main ()
{

int i, j, p;
int num =2;    //Row and column number to be deleted

vector<vector<int> > k;

for(i = 0; i <=5; ++i) 				//Fill vector k
	{
	k.push_back(vector<int>());
	for(j = 1; j <=6; j++)
	k[i].push_back(j);
		}

for (i=0; i< k.size(); ++i)			//Erases row number 2
		{
		if (i == num)
			{
			k.erase(k.begin()+i);
			}
		}


for (int x=0; x< k.size(); ++x)		//print vector
	{
	for (int y=0; y< k[x].size(); ++y)
		{
		cout << k[x][y] <<"\t";			
		}
	cout << endl;
	}							

My attempt to delete a column isn't working:

for (int r=0; r< k.size(); ++r)						
		{
		for (int s=0; s< k[r].size(); ++s)
			{
			if (k[r][s]==k[r][num])
				{
				k.erase(k.begin() +s);
				}
			}
		}		

[Zaita]

Your logic is wrong. k.erase(X) will aways delete a row. Assuming k[Row][Col]. Your use of single letters for naming objects is hideous.

You're also using way too much iteration in your code.

To delete a row:

unsigned rowToDelete = 2;
if (myVector.size() > rowToDelete)
{
  myVector.erase( myVector.begin() + rowToDelete );
}

To delete a column:

unsigned columnToDelete = 2;

for (unsigned i = 0; i < myVector.size(); ++i)
{
  if (myVector[i].size() > columnToDelete)
  {
    myVector[i].erase(myVector[i].begin() + columnToDelete);
  }
}

[asput]

Thank you very much! Sorry about the single letter names. I used them for simplicity, but they obviously don't read well.

[Zaita]

Simplicity is having names that correspond nicely to the functionality of the object. When you put your code down for 6mnths and come back too it; how easy will it be to read and follow?

All good (or even average) coding standards will emphasize the naming of variables to be applicable to their purpose.

[Duthomhas]

Fun:

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

template <typename ContainerType, typename ContainerType::size_type N>
struct delete_column
  {
  void operator () ( ContainerType& container )
    {
    typename ContainerType::iterator iter = container.begin();
    std::advance( iter, N );
    container.erase( iter );
    }
  };

const char* DATA[ 4 ][ 4 ] = 
  {
  { "0,0", "0,1", "0,2", "0,3" },
  { "1,0", "1,1", "1,2", "1,3" },
  { "2,0", "2,1", "2,2", "2,3" },
  { "3,0", "3,1", "3,2", "3,3" },
  };

std::ostream& operator << ( std::ostream& outs, const std::vector <std::vector <std::string> > & v )
  {
  for (unsigned r = 0; r < v.size(); r++)
    {
    outs << "Row " << r << ":  ";
    for (unsigned c = 0; c < v[ r ].size(); c++)
      outs << v[ r ][ c ] << " ";
    outs << std::endl;
    }
  return outs;
  }

int main( int argc, char** argv )
  {
  using namespace std;
  vector <vector <string> > data;

  for (unsigned n = 0; n < 4; n++)
    data.push_back( vector <string> ( DATA[ n ], DATA[ n ] + 4 ) );

  cout << data << endl;

  cout << "Row 2 deleted:\n";
  data.erase( data.begin() + 2 );
  cout << data << endl;

  cout << "Column 3 deleted:\n";
  for_each( data.begin(), data.end(), delete_column <vector <string>, 3> () );
  cout << data << endl;

  cout << "Column 1 deleted:\n";
  for_each( data.begin(), data.end(), delete_column <vector <string>, 1> () );
  cout << data << endl;

  cout << "Column 0 deleted:\n";
  for_each( data.begin(), data.end(), delete_column <vector <string>, 0> () );
  cout << data << endl;

  cout << "Column 2 deleted:\n";
  for_each( data.begin(), data.end(), delete_column <vector <string>, 0> () );  // it's really column 0 now...
  cout << data << endl;

  return 0;
  }