Tom's Merge Sort

tom_merge.cpp

void MultiSort::mergeSort ( CSVFile &csv, vector<int> &keys )
{
        //If vector size is 1, return
        if (csv.get_numRows() <= 1)
        {
                return;
        }
 
        //Else split into two separate subvectors
        CSVFile left;
        CSVFile right;
        int middle = csv.get_numRows() / 2;
 
        for (int i = 0; i < middle; i++ )
        {
                left.add ( csv.get_row(i) );
        }
        for (int j = middle; j < csv.get_numRows(); j++)
        {
                right.add ( csv.get_row(j) );
 
        }
        //Call mergesort to split until subvector size is 1
        mergeSort(left, keys);
        mergeSort(right, keys);
 
        //Merge subvectors returned from prior calls to mergesort
        //Return the resulting merged subvector
        csv = merge(left, right, keys);
 
}               /* -----  end of method MultiSort::mergeSort  ----- */
 
CSVFile MultiSort::merge ( CSVFile &left, CSVFile &right, vector<int> &keys )
{
        CSVFile result;
        while ( left.get_numRows() > 0 || right.get_numRows() > 0 )
        {
                if ( left.get_numRows() > 0 && right.get_numRows() > 0 )
                {
                        if ( left.get_field_range(0, keys) <=
                                        right.get_field_range(0, keys) )
                        {
                                result.add ( left.get_row(0) );
                                left.erase( left );
                        }
                        else
                        {
                                result.add ( right.get_row(0) );
                                right.erase ( right );
                        }
                }
                else if ( left.get_numRows() > 0 )
                {
                        result.add ( left.get_row(0) );
                        left.erase ( left );
                }
                else if ( right.get_numRows() > 0 )
                {
                        result.add ( right.get_row(0) );
                        right.erase ( right );
                }
        }
        return result;
}               /* -----  end of method MultiSort::merge  -----  */
 
/* It crashes when trying to erase from right towards the end of the sort routine. Here's the erase function */
 
void CSVFile::erase ( CSVFile csv )
{
        cout << "deleting ";
        cout << rows[row] << endl;
        rows.erase( rows.begin() + csv.begin());
        numRows--;
}

void CSVFile::erase ( CSVFile &csv )
{
    vector<string>::iterator it = rows.begin();
    cout << "deleting ";
        rows.erase( it );
        numRows--;  
}