Pass data object inside the secondary axis

I have below ggplot

library(ggplot2)
ggplot(faithfuld, aes(waiting, eruptions, z = density)) +
    geom_raster(aes(fill = density)) +
    geom_contour(colour = "white", binwidth = 0.002) +    
    scale_y_continuous(expand = c(0,0), n.breaks = 7, sec.axis = sec_axis(transform = ~ round(., 5), name = "eruptions", breaks = seq(min(eruptions),max(eruptions),length.out = 9))) +
    theme(axis.text.y.left = element_blank(), axis.ticks.y.left = element_blank(), axis.title.y.left = element_blank())

Above code fails to generate any plot because due to seq(min(eruptions),max(eruptions),length.out = 9)

How can I pass data inside the secondary axis without explicitly define outside of the ggplot chain?

Appreciate your pointer.

I don't think breaks= can take a ~-programmatic entry the way that they do for other elements. You can use with(faithfuld, ...) inline:

data("faithfuld", package="ggplot2")
ggplot(faithfuld, aes(waiting, eruptions, z = density)) +
    geom_raster(aes(fill = density)) +
    geom_contour(colour = "white", binwidth = 0.002) +    
    scale_y_continuous(
      expand = c(0,0), n.breaks = 7,
      sec.axis = sec_axis(
        transform = ~ round(., 5), name = "eruptions",
        breaks = with(faithfuld, seq(min(eruptions), max(eruptions), length.out = 9)) )
    ) +
    theme(axis.text.y.left = element_blank(), axis.ticks.y.left = element_blank(), axis.title.y.left = element_blank())

However ... with what you're doing, it seems easier to work with the primary axis and move it to the right by using position="right" instead of a secondary axis:

ggplot(faithfuld, aes(waiting, eruptions, z = density)) +
    geom_raster(aes(fill = density)) +
    geom_contour(colour = "white", binwidth = 0.002) +    
    scale_y_continuous(
      expand = c(0,0), n.breaks = 7, position = "right"
    )