I have created a stacked bar chart where the dimension for the color of the stacked bars is selected from a drop down. (Can be Country, Fruit Name, etc.)
In the legend box I want to show colors assigned to fruit names. This shows fine when bars are stacked by fruit name
Fruit Name
* apple
* lemon
* ...
but otherwise is undefined
Fruit Name
* undefined
How can I force the legend to draw always?
Why do I want to do that? I would like to make the legend interactive, so that you can use it for filtering of the data shown in the graph. That way I could select - say - apple and plum in the legend but stack the bars by country or the order status. (Nice for data exploration.)