code: public void applyColumnFilter(String column, ChangeValue changeValue) throws Exception {
  		for (String row : rowLookup.keySet()) {
  			String oldValue = this.getCell(row, column);
  			String newValue = changeValue.change(oldValue);
  			this.addCell(row, column, newValue);
  		}
  	}
docs: Apply filter to a column to change values from say numberic to nominal
  based on some range
  
  @param column
  @param changeValue
  @throws Exception