How do I add Gantt-chart features to a ggplot - r

Question

I have a chart of a single person's blood pressure readings. I also know when they started and stopped various anti-hypertensive medications and the doses thereof.
How do I add a box above the blood pressure data to show when any particular drug was started and stopped and restarted and at what dose?
Here is a made-up drawing of what I am trying to do.
I could probably use the ggtext package but it looks as if it will be a lot of finnicky messing around for what I want to do. Is there a package that specifically adds this sort of functionality.

Answer 1

This seems like it could be usecase for Paul Murrell's {gggrid} package on github. The package allows you to flexibly draw anything in ggplot2/grid hybrid fashion.
Based on your plot, I'm assuming you have data roughly in the following shapes:
library(ggplot2)
library(gggrid) # remotes::install_github("pmur002/gggrid")
#> Loading required package: grid
df <- data.frame(
x = seq(Sys.Date(), Sys.Date() + 60, by = 1),
y = cumsum(rnorm(61))
)
Along with some annotations for the treatments.
annotation <- data.frame(
label = c("Cardelevovol", "Lisinopril 50 mg", "Lisonopril 100 mg"),
xmin = Sys.Date() + c(0, 0, 40),
xmax = Sys.Date() + c(40, 20, 60),
y = c(1, 0, 0),
fill = c("red", "white", "white")
)
We can then define a function that will draw labelled rectangles in the upper margin of the plot.
annotate_fun <- function(data, coords) {
textheight <- unit(1, "lines")
rectangles <- rectGrob(
x = (coords$xmin + coords$xmax) / 2,
width = coords$xmax - coords$xmin,
y = (data$y + 0.5) * textheight + unit(1, "npc"),
height = textheight,
gp = gpar(fill = coords$fill)
)
text <- textGrob(
label = data$label,
x = (coords$xmin + coords$xmax) / 2,
y = (data$y + 0.5) * textheight + unit(1, "npc")
)
gList(rectangles, text)
}
Which we can then feed to the gggrid::grid_panel() function.
ggplot(df, aes(x, y)) +
geom_point() +
geom_smooth(method = "loess", formula = y ~ x) +
grid_panel(
annotate_fun, data = annotation,
aes(xmin = xmin, xmax = xmax,
label = label, fill = I(fill), x = NULL)
) +
# Turn off clipping and add some extra margin in top
coord_cartesian(clip = "off") +
theme(plot.margin = margin(35, 5.5, 5.5, 5.5))
#> Warning: Ignoring unknown aesthetics: xmin, xmax, label, fill
Created on 2021-10-07 by the reprex package (v2.0.1)