获取绘图区域ggplot2的笛卡尔坐标

我想将标签放置在图例附近。

在下面的代码中，我使用了硬编码的(x,y)值geom_label来获取当前数据帧的所需结果：

#  Creating dataframe
library(ggplot2)
values <- c(rep(0,2), rep(2,3), rep(3,3), rep(4,3), 5, rep(6,2), 8, 9, rep(11,2) )
obs_number <- c(rep(18,18))
value_1 <- c(rep(4,18))
value_2 <- c(rep(7,18))
value_3 <- c(rep(3,18))
  
data_to_plot <- data.frame(values, obs_number, value_1, value_2, value_3)

#  Calculate max frequency value for using in `geom_label`

frequency_count <- data_to_plot %>% group_by(values) %>% count()%>% arrange(n)
max_frequency <- max(frequency_count$n)

# Plot
ggplot(data_to_plot, aes(x = values)) +
  geom_histogram(aes(y = ..count..), binwidth = 1, colour= "black", fill = "white") +
  geom_density(aes(y=..count..), fill="blue", alpha = .25)+
  
  
  geom_vline(aes(xintercept = value_1),
             color="red", linetype = "dashed", size = 0.5, alpha = 1) +
  
  geom_vline(aes(xintercept = value_1),
             color="forestgreen", linetype="dashed", size = 0.5, alpha = 1) +
  
  
  geom_vline(aes(xintercept = value_3),
             color="purple", linetype = "dashed", size = 0.5, alpha = 1) +
  
  
  geom_label(aes(label = obs_number, y = max_frequency*0.87, x = (max(values) - 2.2), color = 'blue'), size = 3.5, alpha = 1) +
  geom_label(aes(label = value_1, y = max_frequency * 0.83, x = (max(values) - 2.2 ), color = 'forestgreen'), size = 3.5, alpha = 1) +
  geom_label(aes(label = value_2, y = max_frequency * 0.79, x = (max(values) - 2.2) , color = 'purple'), size = 3.5, alpha = 1) +
  geom_label(aes(label = value_3, y = max_frequency * 0.75, x = (max(values) - 2.2) , color = 'red'), size = 3.5, alpha = 1) +
  
  
  scale_color_manual(name="Values", 
                     labels = c("Observations number",
                                "value_1",
                                "value_2",
                                "value_3"
                     ), 
                     
                     values = c( "blue",
                                 "forestgreen",
                                 "purple",
                                 "red")) +
  
  labs(title = "relevant_title", y = "Distribution fors DLT values", x = "DLT for the route: average values per batch") +
  theme(plot.title = element_text(hjust = 0.5), 
        axis.title.x = element_text(colour = "darkblue"),
        axis.text.x = element_text(face="plain", color="black", 
                                   size=10, angle=0),
        axis.title.y = element_text(colour = "darkblue"),
        axis.text.y = element_text(face="plain", color="black", 
                                   size=10, angle=0),
        legend.position = c(.90, .80)
  )+
  
  
  labs(title="DLT values", y = "frequency", x = "days")+
  scale_x_continuous(breaks = seq(0, max(data_to_plot$values), 1))

这是理想的结果：

但这不适用于所有数据集。

题：

如何获得绘图区域的笛卡尔坐标，因此我将替换max_frequency并max(values)在geom_label其中插入标签并使其与图例对齐legend.position = c(.90, .80)。

也欢迎其他选择。