How to use ggplot in a loop with computed parameters? - r

Question

I am trying to produce a variable number of rectangles (layers) in a ggplot of a zoo object. I would like to do this in a loop since I do not know ahead of time how many rectangles I will need. Here is a toy example.
library("zoo")
library("ggplot2")
set.seed(1)
y <- runif(50, min = 1, max = 2)
start <- as.numeric(as.Date("2018-01-01"))
x <- as.Date(start:(start + 49))
x.zoo <- zoo(y, order.by = x)
## Fill areas
bars <- data.frame(start = c(x[5], x[20], x[35]),
end = c(x[10], x[25], x[40]))
I can plot these manually with this code:
## Plot manually
print(autoplot.zoo(x.zoo, facets = NULL) +
geom_rect(aes(xmin = bars[1,1],
xmax = bars[1,2], ymin = -Inf, ymax = Inf),
fill = "pink", alpha = 0.01) +
geom_rect(aes(xmin = bars[2,1],
xmax = bars[2,2], ymin = -Inf, ymax = Inf),
fill = "pink", alpha = 0.01) +
geom_rect(aes(xmin = bars[3,1],
xmax = bars[3,2], ymin = -Inf, ymax = Inf),
fill = "pink", alpha = 0.01))
This gives me this desired image:
I tried using the loop below but it only plots the last bar. How do I do this??
## This didn't work but illustrates what I am trying to do
p = autoplot.zoo(x.zoo, facets = NULL)
for(i in 1:3) {
p = p + geom_rect(aes(xmin = bars[i,1],
xmax = bars[i,2], ymin = -Inf, ymax = Inf),
fill = "pink", alpha = 0.01)
}
print(p)

Answer 1

You don't need a loop. geom_rect is vectorised
autoplot.zoo(x.zoo, facets = NULL) +
geom_rect(aes(xmin = start, xmax = end, ymin = -Inf, ymax = Inf), data = bars, fill = "pink", alpha = 0.4, inherit.aes = FALSE)

Answer 2

One way to avoid the for loop is to convert x.zoo into a data.frame and map the data to geom_line. This way, you can map the bars data to geom_rect separately.
dat <- data.frame(index = index(x.zoo), data.frame(x.zoo))
ggplot() +
geom_rect(data = bars, aes(xmin = start, xmax = end, ymin =-Inf, ymax = Inf), fill = 'pink', alpha = .5) +
geom_line(data=dat, aes(x = index, y = x.zoo))