Allow plotting of gates without data

[jacobpwagner]

Occasionally a use case arises where it is helpful to be able to plot gates using geom_gate without any underlying data present, just to visually inspect the gate definitions. However, this cannot be accomplished with the current ggcyto method framework without a bit of a hacky workaround. If you try providing a mapping without providing data (e.g. ggcyto(mapping=aes("FSC-H, "SSC-H")), the call ends up here because data=NULL:

ggcyto/R/fortify_fs.R

Lines 27 to 30 in 5ced2c1

	fortify_fs.default <- function(model, data, ...) {
	stop("ggcyto doesn't know how to deal with data of class ", class(model), call. = FALSE)
	}

One workaround is to just give the ggcyto call a dummy flowFrame to work with, but we can't expect users to know to do this:

library(flowCore)
library(flowWorkspace)
library(CytoML)
library(ggcyto)
ws <- open_flowjo_xml(system.file("extdata", "manual.xml", package="flowWorkspaceData"))
gs <- flowjo_to_gatingset(ws, name=2, execute=FALSE)
gate <- gh_pop_get_gate(gs[[1]], "singlets")
dummy <- matrix(as.numeric(c(0,0)), nrow = 1, ncol = 2) # Needs at least one row bc of some min/max calls...
gate_dims <- colnames(gate@boundaries)
colnames(dummy) <- gate_dims
fr <- flowFrame(dummy)
ggcyto(fr, aes_(gate_dims[[1]], gate_dims[[2]])) + 
  geom_gate(gate) + 
  ggcyto_par_set(limits=list(x=c(0,max(gate@boundaries[,1])), y=c(0,max(gate@boundaries[,2]))))

An easy first fix that would have minimal ramifications would be to make a function to wrap up similar logic to just plot a gate. Ideally, we could incorporate this in to the structure of the ggcyto call dispatch, but that requires more careful consideration.