report a bug in ScaleBinned$get_breaks()

[microly]

hi, @thomasp85
Firstly, thank you for your hard works to improve ggplot2!

I think there is a small bug in ScaleBinned$get_breaks(), which is in:

ggplot2/R/scale-.r

Lines 991 to 993 in 115c396

	} else if (is.function(self$breaks)) {
	breaks <- self$breaks(limits, self$n_bins)
	} else {

As I known, end users has no way to set the value of ScaleBinned$n_bins, which has a NULL value by default.
So, when the breaks is a function provided by users, the function's second parameter will always set to be NULL.
As a consequence, users cannot get meaningful breaks by set breaks as a function in the scales, such as scale_colour_stepsn.

This is a simple example:

df <- data.frame(
    x = runif(100),
    y = runif(100),
    z = rnorm(100)
)

brk <- function(limits, n_bins) {
    if (is.null(n_bins))
        stop("n_bins is always set to be NULL, users cannot implement useful function for breaks.")
    else cat("users can set the value of n_bins, and get meaningful breaks using the values of limits and n_bins.")
}

library(ggplot2)

ggplot(df, aes(x, y)) +
    geom_point(aes(colour = z)) +
    scale_colour_stepsn(colours = terrain.colors(10), breaks = brk)

# Error in f(...) : 
# n_bins is always set to be NULL, users cannot implement useful function for breaks. 

I will opening a pull request for this bug, please consider it, thanks!

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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/