[SOLVED] How to use a value of a variable as subscripted text in an automated annotation to ggplot

How to use a value of a variable as subscripted text in an automated annotation to ggplot

I'd like to add an annotation to my geom_density_ridges() plot which inidicates the defined limit for scale_x_continous()

In the example below there is some data to build the plot. The annotation named grob1 leads to the kind of annotation I would like to achieve unsing the value of variable limit_quantile. (The plots shall later on be drawn within a call of one of the apply-familie functions where different variables of my original data set need different plot parameters for a better readability of pthe lots.)

Is there a way to use the value of the variable limit_quantile may even a helper variable from as.character(limit_quantile) as text input? Or are ther other ways to achieve an automation friendly creation of a subscipt text in annotations?

## I like to add a subscript text from a variable value
# 2022-DEC-02


df1 <- data.frame(v1 = c(1:100), class = 1, v2 = rnorm(100) )
df2 <- data.frame(v1 = c(1:100), class = 2, v2 = rnorm(100)*5+10 )
df3 <- data.frame(v1 = c(1:100), class = 3, v2 = rnorm(100)*10+25 )

df <- rbind(df1,df2,df3)


limit_quantile <- 0.99

ridge_plot <- ggplot(df, aes(x = v2, y = as.factor(class), group = as.factor(class))) + 
    geom_density_ridges(stat = "binline", rel_min_height = 0.005 , binwidth = 1,  alpha = 0.5,scale = 0.99) +
    scale_y_discrete(expand = c(0.01, 0), breaks = c(1:3)) +
    scale_x_continuous(expand = c(0.01, 0), limits = quantile(df$v2, c(0, limit_quantile))) +
    theme_ridges() +
    #ylab("Relative Häufigkeit je Teilbauflächenklasse") +
    xlab("Values of v2") +
    ylab(NULL) +
    theme(axis.title.x = element_text(hjust = 0.5))


grob1 <- grobTree(textGrob(bquote("X-Axis-Limit: Q"[0.95]), x=0.9,  y=0.1, hjust=1,
                           gp=gpar(fontsize = 10.5, fontface="italic")))

ridge_plot_text1 <- ridge_plot  + annotation_custom(grob1)
ridge_plot_text1

grob2 <- grobTree(textGrob(bquote("X-Axis-Limit: Q"[limit_quantile]), x=0.9,  y=0.1, hjust=1,
                           gp=gpar(fontsize = 10.5, fontface="italic")))
ridge_plot_text2 <- ridge_plot  + annotation_custom(grob2)
ridge_plot_text2

# Credits for annotation: http://www.sthda.com/english/wiki/ggplot2-texts-add-text-annotations-to-a-graph-in-r-software
# Credits for bquote():   https://www.geeksforgeeks.org/superscript-and-subscript-axis-labels-in-ggplot2-in-r/

I tried to pass the value as charachter to the bquote(): limit_quantile_text <- as.character(limit_quantile), but that did not change the behaviour if bquote() and textGrob()


 grobTree(textGrob(bquote("X-Axis-Limit: Q"[limit_quantile_text ]), x=0.9,  y=0.1, hjust=1,
                           gp=gpar(fontsize = 10.5, fontface="italic")))

In addition I tried the use of get(), which works when defining aes()-elements

#second try
grob2 <- grobTree(textGrob(bquote("X-Axis-Limit: Q"[get(limit_quantile)]), x=0.9,  y=0.1, hjust=1,
                           gp=gpar(fontsize = 10.5, fontface="italic")))

Solution

The examples here made the correct bquote() syntax clear to me now. A variable containing character values/ a string can be used by a .() notation. So for the example above the code is:

grob2 <- grobTree(textGrob(bquote("X-Axis-Limit: Q"[.(limit_quantile)]), x=0.9,
  y=0.1, hjust=1,
 gp=gpar(fontsize = 10.5, fontface="italic")))