Visualize secondary grouping
From Nathan Stutzman (nbstutzman@ucsd.edu) by email:
Secondary Grouping: For a lot of my data, I have two dimensions in my grouping scheme and it would be nice to visualize both at the same time. For example, my primary grouping may be by treatment, but I may also be comparing those treatments across timepoints. Right now the best way I can visualize both at once is to group by one and then filter/select by the other grouping, but this isn't the best since I can only show one selection at a time and the selected points black out the other grouping.