annotate ggplot above plot - r

Question

I tried lately to annotate a graph with boxes above a ggplot.
Here is what I want:
I found a way using grid, but I find it too complicated, and I am quite sure there is a better way to do it, more ggplot2 friendly. Here is the example and my solution:
the data:
y2 <- 350
mesure_pol <- data.frame(x1 = c(1,4,7),
x2 = c(4,7,10),
politiquecat = c(1:3),
politique = c("Phase 1\n","Phase 2\n","Phase 3\n"),
y = c(y2,y2,y2)
)
mesure_pol$x_median <- (mesure_pol$x1 + mesure_pol$x2)/2
colorpal <- viridis::inferno(n=3,direction = -1)
plot
the main plot
p <- ggplot(data = mesure_pol) +
geom_rect(aes(xmin = x1,
xmax = x2,
ymin = 0,
ymax = 300,
fill = as.factor(politiquecat)),
fill = colorpal,
color = "black",
size = 0.3,
alpha = 0.2)+
theme(plot.margin=unit(c(60, 5.5, 5.5, 5.5), "points"))+
coord_cartesian(clip = 'off')
the annotation part
Here is the part I am not happy with:
for (i in 1:dim(mesure_pol)[1]) {
text <- textGrob(label = mesure_pol[i,"politique"], gp = gpar(fontsize=7,fontface="bold"),hjust = 0.5)
rg <- rectGrob(x = text$x, y = text$y, width = stringWidth(text$label) - unit(3,"mm") ,
height = stringHeight(text$label) ,gp = gpar(fill=colorpal[i],alpha = 0.3))
p <- p + annotation_custom(
grob = rg,
ymin = mesure_pol[i,"y"], # Vertical position of the textGrob
ymax = mesure_pol[i,"y"],
xmin = mesure_pol[i,"x_median"], # Note: The grobs are positioned outside the plot area
xmax = mesure_pol[i,"x_median"]) +
annotation_custom(
grob = text,
ymin = mesure_pol[i,"y"], # Vertical position of the textGrob
ymax = mesure_pol[i,"y"],
xmin = mesure_pol[i,"x_median"], # Note: The grobs are positioned outside the plot area
xmax = mesure_pol[i,"x_median"])
}
Is there a simplier/nicer way to obtain similar result ? I tried with annotate, label but without any luck.

Answer 1

An alternative approach to achieve the desired result would be to make the annotations via a second ggplot which could be glued to the main plot via e.g. patchwork.
For the annotation plot I basically used your code for the main plot, added a geom_text layer, get rid of the axix, etc. via theme_void and set the limits in line with main plot. Main difference is that I restrict the y-axis to a 0 to 1 scale. Besides that I shifted the xmin, xmax, ymin and ymax values to add some space around the rectangels (therefore it is important to set the limits).
library(ggplot2)
library(patchwork)
y2 <- 350
mesure_pol <- data.frame(x1 = c(1,4,7),
x2 = c(4,7,10),
politiquecat = c(1:3),
politique = c("Phase 1\n","Phase 2\n","Phase 3\n"),
y = c(y2,y2,y2)
)
mesure_pol$x_median <- (mesure_pol$x1 + mesure_pol$x2)/2
colorpal <- viridis::inferno(n=3,direction = -1)
p <- ggplot(data = mesure_pol) +
geom_rect(aes(xmin = x1,
xmax = x2,
ymin = 0,
ymax = 300,
fill = as.factor(politiquecat)),
fill = colorpal,
color = "black",
size = 0.3,
alpha = 0.2)
ann <- ggplot(data = mesure_pol) +
geom_rect(aes(xmin = x1 + 1,
xmax = x2 - 1,
ymin = 0.2,
ymax = 0.8,
fill = as.factor(politiquecat)),
fill = colorpal,
color = "black",
size = 0.3,
alpha = 0.2) +
geom_text(aes(x = x_median, y = .5, label = politique), vjust = .8, fontface = "bold", color = "black") +
coord_cartesian(xlim = c(1, 10), ylim = c(0, 1)) +
theme_void()
ann / p +
plot_layout(heights = c(1, 4))

Answer 2

By setting a second x-axis and filling the background of the new axis labels with element_markdown from the ggtext package. You may achieve this:
Here is the code:
library(ggtext)
y2 <- 350
mesure_pol <- data.frame(x1 = c(1,4,7),
x2 = c(4,7,10),
politiquecat = c(1:3),
politique = c("Phase 1\n","Phase 2\n","Phase 3\n"),
y = c(y2,y2,y2)
)
mesure_pol$x_median <- (mesure_pol$x1 + mesure_pol$x2)/2
p <- ggplot(data = mesure_pol) +
geom_rect(aes(xmin = x1,
xmax = x2,
ymin = 0,
ymax = 300,
fill = as.factor(politiquecat)),
fill = c("yellow", "red", "black"),
color = "black",
size = 0.3,
alpha = 0.2) +
scale_x_continuous(sec.axis = dup_axis(name = "",
breaks = c(2.5, 5.5, 8.5),
labels = c("Phase 1", "Phase 2", "Phase 3"))) +
theme(plot.margin=unit(c(60, 5.5, 5.5, 5.5), "points"),
axis.ticks.x.top = element_blank(),
axis.text.x.top = element_markdown(face = "bold",
size = 12,
fill = adjustcolor(c("yellow", "red", "black"),
alpha.f = .2)))+
coord_cartesian(clip = 'off')