ggplot - facet by function output

Question

I\'m unsure how to facet by a function of the data in the data element of a ggplot object. In the following toy example, what I want to do is some

Answer 1

this sounds familiar to me, but I never managed to fix it - I think facet variable handling is just less powerful than aesthetic variable handling.

Addressing your root requirement - to ad-hoc facet an existing ggplot; note that you can replace wholesale the (master) data set of an existing R ggplot - for instance

myplot %+% transform(myplot$data, z=z%%2)