Grob参数从data.frame到ggplot2

如何将一组grob（ximin、xmax、ymin、ymax）的参数从data.frame传递到annotation_自定义函数（ggplot2）。下面的示例说明了该问题

# Grobs
a <- ggplot(diamonds, aes(carat)) + geom_histogram(fill = "red") + theme_void()
g1 <- ggplotGrob(a)
b <- ggplot(diamonds, aes(carat)) + geom_histogram(fill = "blue") + theme_void()
g2 <- ggplotGrob(b)

# Structure of the arguments location
my.data <- data.frame(grob = c("g1", "g2"), xmin = c(1.5, 5.5), xmax = c(4.5, 8), 
                  ymin = c(2.5, 4), ymax = c(6, 8))

# Desired result
df <- data.frame(x = 1:10, y = 1:10)
ggplot(df, aes(x, y)) + geom_blank() + theme_bw() +
annotation_custom(g1, xmin = 1.5, xmax = 4.5, ymin = 2.5, ymax = 6) +
annotation_custom(g2, xmin = 5.5, xmax = 8, ymin = 4, ymax = 8)

#Grobs
a使用
geom_custom（）
会更自然，但同时您可以创建一个图层列表

my.data <- data.frame(xmin = c(1.5, 5.5), xmax = c(4.5, 8), 
                      ymin = c(2.5, 4), ymax = c(6, 8))
my.data$grob <- list(g1,g2)
get_grob <- function(grob, xmin, xmax, ymin, ymax){
  annotation_custom(grob=grob[[1]], xmin=xmin, xmax=xmax, ymin=ymin, ymax=ymax)
}
df <- data.frame(x = 1:10, y = 1:10)
ggplot(df, aes(x, y)) + geom_blank() + theme_bw() +
  plyr::mlply(my.data, get_grob)

my.data