stat_contour's breaks parameter is undocumented

[alistaire47]

When trying to use geom_contour to draw lines at specific levels à la contour(..., levels = ...), I discovered this SO answer which documents that geom_contour can be passed a breaks parameter to specify particular z values where contour lines should be drawn.

Weirdly, this behavior is not documented in ?geom_contour, ?geom_density_2d, ?layer, or ?ggplot2:::StatContour, and taking a cursory look at the source, I'm not sure where the breaks parameter is picked up. Given the behavior is important enough to merit a parameter in contour, seems like it should be in the docs.

I can make a PR if you like, but the problem is that I'm not exactly sure how this behavior should be documented, as I'm not sure what breaks is a parameter of. An example wouldn't be too hard to add, though.

Reprex:

library(ggplot2)

v <- ggplot(faithfuld, aes(waiting, eruptions, z = density)) 

v + geom_contour()

v + geom_contour(breaks = c(0.002, 0.02))

[clauswilke]

The bins, binwidth, breaks, and complete parameters are parameters of stat_contour():

ggplot2/R/stat-contour.r

Lines 37 to 38 in d3bd92e

	compute_group = function(data, scales, bins = NULL, binwidth = NULL,
	breaks = NULL, complete = FALSE, na.rm = FALSE) {

(complete has no effect, though, as far as I can tell.)

They should be documented just like the comparable parameters in stat_bin(), and they should probably also be added to the stat_contour() constructor (again, just like in stat_bin()):

ggplot2/R/stat-bin.r

Lines 42 to 49 in d3bd92e

	stat_bin <- function(mapping = NULL, data = NULL,
	geom = "bar", position = "stack",
	...,
	binwidth = NULL,
	bins = NULL,
	center = NULL,
	boundary = NULL,
	breaks = NULL,

[JHonaker]

I'll take a stab at fixing this.

[paleolimbot]

This TDD issue is a relatively easy fix! The open PR on this (#2926) has been abandoned and needs a few fixes, notably that

      bins = NULL,
      binwidth = NULL,
      breaks = NULL,

(in geom-contour.r) needs to be

      bins = bins,
      binwidth = binwidth,
      breaks = breaks,

(or else the user-specified bins value won't be passed on to the stat/geom), and the documentation needs to be built with devtools::document(). A fresh PR should fix this nicely!

[lock]

This old issue has been automatically locked. If you believe you have found a related problem, please file a new issue (with reprex) and link to this issue. https://reprex.tidyverse.org/