Feature request: Ability to pass in a data frame and use facets

[puterleat]

Say you have data like this:

   day bugs spiders worms
1    0    51        49        39
2   2    28        72        61
3   3    41        59        48
4  4    42        58        474

It would be great if you could do this:

waffle(df) + facet_grid(month~.)

I think the default behaviour if you don't add the facet should be to take the mean across days.