public List<DoubleStringMapping> toStringMappings()
{
List<DoubleStringMapping> list = new ArrayList<DoubleStringMapping>(numCols * numRows);
for( T col : colIndexes ) for( S row : rowIndexes )
if( get( col, row ) != initial )
list.add( new DoubleStringMapping( col, row, get( col, row ) ) );
return list;
}