Question

I wrote the following function to make a 2-D array object odd-dimensioned by adding a row or column as needed (where sizeX, sizeY, get, set, and resize are self-explanatory grid2D member functions).

void makeOdd(grid2D<double> *pSrc)
// ---------------------------------------------------------------------------------------------------------
// Make one or both dimensions of input array odd (via row/column copy).
{

    // Variable declarations
    grid2D<double> pTmp = *pSrc;                                // Scratch local source variable
    int simax, sjmax;                                               // Source dimensions

    // Get source dimensions
    sjmax = pSrc->sizeY();
    simax = pSrc->sizeX();

    // Check if source is already odd-dimensioned
    if (sjmax%2 && simax%2) return;

    // Extend row/column of source if necessary
    if (sjmax%2 && !(simax%2))                                      // Odd rows, even columns
    {
        pSrc->resize(simax+1,sjmax);                                // Resize source with extra column
        for(int i=0; i<simax+1; i++)
        {
            for(int j=0; j<sjmax; j++)
            {
                if(i==simax)
                    pSrc->set(i,j,pTmp.get(simax-1,j));             // Copy last column
                else
                    pSrc->set(i,j,pTmp.get(i,j));
            }
        }
        return;
    }
    else if (!(sjmax%2) && simax%2)                                 // Even rows, odd columns
    {
        pSrc->resize(simax,sjmax+1);                                // Resize source with extra row
        for(int i=0; i<simax; i++)
        {
            for(int j=0; j<sjmax+1; j++)
            {
                if(i==simax)
                    pSrc->set(i,j,pTmp.get(i,sjmax-1));             // Copy last row
                else
                    pSrc->set(i,j,pTmp.get(i,j));
            }
        }
        return;
    }
    else                                                            // Even rows, even columns
    {
        pSrc->resize(simax+1,sjmax+1);                              // Resize source with extra row and column
        for(int i=0; i<simax+1; i++)
        {
            for(int j=0; j<sjmax+1; j++)
            {
                if(i==simax && j==sjmax)
                {
                    pSrc->set(i,j,pTmp.get(simax-1,sjmax-1));       // Copy last column and row
                }
                else if(i==simax && j<sjmax)
                {
                    pSrc->set(i,j,pTmp.get(simax-1,j));             // Copy last column
                }
                else if(i<simax && j==sjmax)
                {
                    pSrc->set(i,j,pTmp.get(i,sjmax-1));             // Copy last row
                }
                else
                {
                    pSrc->set(i,j,pTmp.get(i,j));
                }
            }
        }
        return;
    }

}

My question: is there a cleaner/more efficient way of doing this?

Many thanks…

Answer 1

I think it would be easier to check the number of rows first, and extend it by 1 if needed. Then, check the number of columns, and extend each of them by 1 if needed.

Assuming your grid2d is a wrapper around a vector<vector<T> >, you can pass a value to resize that it will use to fill the newly created space, so when you add a row, you can just pass current last row to get it copied into the new last row.