@drsimonj here with a quick share on making great use of the secondary y axis with ggplot2 – super helpful if you’re plotting groups of time series!Here’s an example of what I want to show you how to create (pay attention to the numbers of the right):Setup #To setup we’ll need the tidyverse package and the Orange data set that comes with R. This tracks the circumference growth of five orange trees over time.library(tidyverse)d Grouped Data: circumference ~ age | Tree#> Tree age circumference#> 1 1 118 30#> 2 1 484 58#> 3 1 664 87#> 4 1 1004 115#> 5 1 1231 120#> 6 1 1372 142Template code #To create the basic case where the numbers appear at the end of your time series lines, your code might look something like this:# You have a data set with:# - GROUP colum# - X colum (say time)# - Y column (the values of interest)DATA_SET# Create a vector of the last (furthest right) y-axis values for each groupDATA_SET_ENDS % group_by(GROUP) %>% top_n(1, X) %>% pull(Y)# Create plot with `sec.axis`ggplot(DATA_SET, aes(X, Y, color = GROUP)) + geom_line() + scale_x_continuous(expand = c(0, 0)) + scale_y_continuous(sec.axis = sec_axis(~ ., breaks = DATA_SET_ENDS))Let’s see it! #Let’s break it down a bit. We already have our data set where the group colum is Tree, the X value is age, and the Y value is circumference.So first get a vector of the last (furthest right) values for each group:d_ends % group_by(Tree) %>% top_n(1, age) %>% pull(circumference)d_ends#> [1] 145 203 140 214 177Next, let’s set up the basic plot without the numbers to see how each layer adds up.ggplot(d, aes(age, circumference, color = Tree)) + geom_line()Now we can use scale_y_*, with the argument sec.axis to create a second axis on the right, with numbers to be displayed at breaks, defined by our vector of line ends:ggplot(d, aes(age, circumference, color = Tree)) + geom_line() + scale_y_continuous(sec.axis = sec_axis(~ ., breaks = d_ends))This is a great start, The only major addition I suggest is expanding the margins of the x-axis so the gap disappears. You do this with scale_x_* and the expand argument:ggplot(d, aes(age, circumference, color = Tree)) + geom_line() + scale_y_continuous(sec.axis = sec_axis(~ ., breaks = d_ends)) + scale_x_continuous(expand = c(0, 0))Polishing it up #Like it? Here’s the code to recreate the first polished plot:library(tidyverse)d % as_tibble()d_ends % group_by(Tree) %>% top_n(1, age) %>% pull(circumference)d %>% ggplot(aes(age, circumference, color = Tree)) + geom_line(size = 2, alpha = .8) + theme_minimal() + scale_x_continuous(expand = c(0, 0)) + scale_y_continuous(sec.axis = sec_axis(~ ., breaks = d_ends)) + ggtitle("Orange trees getting bigger with age", subtitle = "Based on the Orange data set in R") + labs(x = "Days old", y = "Circumference (mm)", caption = "Plot by @drsimonj")Sign off #Thanks for reading and I hope this was useful for you.For updates of recent blog posts, follow @drsimonj on Twitter, or email me at drsimonjackson@gmail.com to get in touch.If you’d like the code that produced this blog, check out the blogR GitHub repository.