Get cartesian coordinates for plot area ggplot2 - r

Question

I would like to position labels close to the legend.
In the code below I have hardcoded (x,y) values in geom_label to get desired result for the current dataframe:
# 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))
This is desired result:
But this will not work for all datasets.
Question:
How can I get cartesian coordinates of the plot area, so I would replace max_frequency and max(values) in geom_label and align labels with the legend, given that legend.position = c(.90, .80).
Other alternatives are also welcome.

Answer 1

Under the flag of 'alternatives are also welcome': why not use a text glyph for the geom_vline()s and override the actual labels?
I rearranged the code a bit for my own understanding, but here is an example:
library(tidyverse)
#> Warning: package 'tibble' was built under R version 4.0.3
#> Warning: package 'tidyr' was built under R version 4.0.3
#> Warning: package 'readr' was built under R version 4.0.3
#> Warning: package 'dplyr' was built under R version 4.0.3
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)
# Extra dataframe for storing the xintercepts and labels
vals <- data.frame(xintercept = c(18, 4, 7, 3),
label = c("Observations number", "value_1", "value_2", "value_3"))
frequency_count <- data_to_plot %>% group_by(values) %>% count()%>% arrange(n)
max_frequency <- max(frequency_count$n)
ggplot(data_to_plot, aes(x = values)) +
geom_histogram(aes(y = ..count..),
binwidth = 1, colour= "black", fill = "white") +
geom_density(aes(y=..count..),
fill="blue", alpha = .25)+
geom_vline(aes(xintercept = xintercept, color = label),
data = vals[2:nrow(vals), ],
linetype = "dashed", size = 0.5, alpha = 1,
# Give different legend glyph for vlines
key_glyph = draw_key_text) +
scale_color_manual(
name= "Values",
limits = vals$label,
values = c("blue", "forestgreen", "purple", "red"),
# Override the labels and set size to something sensible
guide = guide_legend(override.aes = list(label = vals$xintercept,
size = 3.88))
) +
labs(title = "relevant_title", y = "Distribution fors DLT values",
x = "DLT for the route: average values per batch") +
theme(plot.title = element_text(hjust = 0.5),
axis.title.x = element_text(colour = "darkblue"),
axis.text.x = element_text(face="plain", color="black",
size=10, angle=0),
axis.title.y = element_text(colour = "darkblue"),
axis.text.y = element_text(face="plain", color="black",
size=10, angle=0),
legend.position = c(.90, .80)
)+
labs(title="DLT values", y = "frequency", x = "days")+
scale_x_continuous(breaks = seq(0, max(data_to_plot$values), 1))
Created on 2021-01-08 by the reprex package (v0.3.0)