R GGPLOT2 Alternate panel.background fill with white and grey

Question

I want to create a line plot with the help of ggplot2 and I want to have the panel background colors alternate between white and grey based on the X-axis values.

In this case, DOY is the day of the year and I would like for it to transition between each day.

I have also included some basic sample code:

DOY <- c(1, 2, 3, 4, 5)

Max <- c(200, 225, 250, 275, 300)

sample <- data.frame(DOY, Max)

ggplot()+

  geom_line(data=sample, aes(x=DOY, y=Max), color = "black")

Answer 1

You can add a new variable (called e.g. stripe) to the data, which alternates based on the value of DOY. After that you can use that variable as the basis for filled, transparent rectangles.

I'm assuming that DOY is a sequence of integers with interval = 1, so we can assign on the basis of whether DOY is odd or even.

(Note: sample - not a great variable name as there's a function of that name).

library(dplyr)

library(ggplot2)

sample %>% 

  mutate(stripe = factor(ifelse(DOY %% 2 == 0, 1, 0))) %>% 

  ggplot(aes(DOY, Max)) + 

  geom_point() + 

  geom_rect(aes(xmax = DOY + 1, 

                xmin = DOY, 

                ymin = min(Max), 

                ymax = Inf, 

                fill = stripe), alpha = 0.4) + 

  scale_fill_manual(values = c("white", "grey50")) + 

  theme_bw() + 

  guides(fill = FALSE)

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