Draw something outside of the plot, between the axis and plot area-CodePudding

I have some generic plot with continuous X and categorical Y axis, for example:

data(iris)
p1 <-
  ggplot(iris, aes(y=Species, x=Sepal.Length))  
  geom_violin()

Now I want to annotate it with some labels that should be positioned right next to the Y axis, with a quick-and-dirty solution like this:

df.labels <- data.frame(Species=c('setosa','versicolor','virginica'), Labels=c('labA','labB','labC'))

p2 <- p1   geom_text(data = df.labels, aes(x=4, y=Species, label=Labels))

Note that I had to indicate x=4 explicitly; for more general case I made this function:

add_label <- function(inpPlot, inpData, colLabel){
  plotX1 <- ggplot_build(inpPlot)$layout$panel_params[[1]]$x.range[1]
  plotX2 <- ggplot_build(inpPlot)$layout$panel_params[[1]]$x.range[2]
  plotW <- plotX2 - plotX1
  posX <- plotX1 - 0.05*plotW

  colGrp <- as_label(inpPlot$mapping$y)
    
  inpPlot   
    coord_cartesian(clip='off')  
    geom_text(data = inpData, aes_string(x='posX', y=colGrp, label=colLabel))  
}

p3 <- add_label(p1, df.labels, 'Labels')

What I don't like in this solution:

Offset calculated as "5% of plot width" doesn't work very well when I resize plot window (I would like to have a fixed absolute distance between the axis and the labels)
It doesn't work if my initial plot has coord_cartesian() applied, for example:

p1c <- p1   coord_cartesian(xlim = c(5,NA))
p4 <- add_label(p1c, df.labels, 'Labels')

Labels are shown on the plot area itself, I want them to be outside of the plot area (but "inside" from the Y axis, i.e. to the right from the axis labels).
What I would like to have ideally, is something like this:

p5 <- add_label_good(p1c, df.labels, 'Labels')

i.e. it should draw labels between the axis and plot area, and this space should be of fixed width.
Is there any way at all to achieve this?

CodePudding user response：

You might consider patchwork, with two aligned plots:

library(patchwork)

plot_labels <-  ggplot(df.labels, aes(x = 0, y = Species, label = Labels))  
  geom_text(hjust = 0)  
  theme_void()  
  theme(axis.text.y = element_text(),
        axis.title.y = element_text(angle = 90, margin = margin(0,12,0,0, unit = "pt")))

plot_labels  
  (p1   theme(axis.title.y = element_blank(),
              axis.text.y = element_blank()))  
  plot_layout(widths = c(1,8))

CodePudding user response：

One option is to use facet strips:

p1   facet_grid(Species~., scales = 'free_y', switch = "y",
                labeller = labeller(Species = function(x) {
                  df.labels$Labels[match(x, df.labels$Species)]}))  
  theme(text = element_text(size = 16),
        strip.text.y.left = element_text(angle = 0, face =  "bold",
                                         margin = margin(10, 10, 10, 10)),
        strip.background = element_blank(),
        panel.spacing = unit(0, "mm"))

Another option is to use ggtext::element_markdown() and use the axis text itself as a label:

p1  
  scale_y_discrete(labels = function(x) {
    paste(x, df.labels$Labels[match(x, df.labels$Species)],
          sep = paste0(rep("&nbsp; ", 5), "<b>", collapse = ""))
  })  
  theme(text = element_text(size = 16),
        axis.text.y = ggtext::element_markdown())

For a truly fixed-width text area on the far left of the plot, you could use annotation_custom

p1   
  annotation_custom(grid::rectGrob(x = unit(10, "mm"), y = 0.5,
                                   width = unit(20, "mm"), height = 1,
                                   gp = grid::gpar(col = NA)))  
  annotation_custom(grid::textGrob(df.labels$Labels,
                    x = unit(10, "mm"),
                    y = c(0.81, 0.5, 0.19)))