Charts in wpDataTables have one very useful feature from version 1.7: If you enable this feature the values of the rows with same label will be summed up and rendered as a single series otherwise all rows will be rendered as separate series.
This can be helpful if you have repeating rows with identical name in your table and you want to show them summed in your chart. This feature will also work in combination with Follow table filtering.
It is really simple to activate the grouping for a chart. Just tick this checkbox in the chart create/edit wizard: