r - ggplot : How to retrieve values for axis labels?

Question

如何提取下面ggplot中分别用于标记y和x轴的数字(分别为20, 30, 40和10 , 15 ,20 ,25, 30, 35)？

情节

从r-statistics.co



可复制的代码

# Scatterplot
theme_set(theme_bw())  # pre-set the bw theme.
g <- ggplot(mpg, aes(cty, hwy))
g + geom_count(col="tomato3", show.legend=F) +
  labs(subtitle="mpg: city vs highway mileage", 
       y="hwy", 
       x="cty", 
       title="Counts Plot")

我尝试查看 str(g)的输出，但是效果不佳。

Answer 1

基于CPak的答案，ggplot2_3.0.0的结构略有变化。现在可以使用以下方式提取标签:

ggplot_build(g)$layout$panel_params[[1]]$y.labels
#[1] "20" "30" "40" 
ggplot_build(g)$layout$panel_params[[1]]$x.labels
#[1] "10" "15" "20" "25" "30" "35"

编辑:
从 ggplot2_3.3.0开始，使用以下命令找到标签:

# check package version
utils::packageVersion("ggplot2")

y_labs <- ggplot_build(g)$layout$panel_params[[1]]$y$get_labels()
y_labs[!is.na(y_labs)]
#[1] "20" "30" "40"
x_labs <- ggplot_build(g)$layout$panel_params[[1]]$x$get_labels()
x_labs[!is.na(x_labs)]
#[1] "10" "15" "20" "25" "30" "35"