Align ggplot y axis labels along common middle line, across facets

July 17, 2023

When y-axis labels are of different length, element_text(hjust = .5) aligns the labels around a common middle line within facets, rather than across all the labels.

An example:

library(tidyverse)

t1 <- tibble(
  labs = c(
    "A short label",
    "Second short label",
    "This is a medium length label",
    "This is also a medium length",
    "Now, this label is actually quite long, really long",
    "This label is also actually quite long, really long"
    ) %>% 
    fct_inorder %>% 
    fct_rev,
  facs = str_c(
    "facet", 1:3
    ) %>% 
    rep(each = 2),
  x = runif(6)
  )

t1 %>% 
  ggplot(
    aes(
      x, labs
    )
  ) +
  geom_point() +
  facet_grid(
    vars(facs), 
    scales = "free_y"
  ) +
  labs(
    x = "",
    y = ""
  ) +
  theme(
    axis.text.y = element_text(hjust = .5)
  )

should return

How do I get the y-axis labels to be middle aligned along a common axis?

>Solution :

You could add the following dplyr::mutate to the tibble: mutate(labs = str_pad(labs, max(str_width(labs)), side = "both")) to add padding to the strings so they all have the same apparent length.

library(tidyverse)

t1 <- tibble(
  labs = c(
    "A short label",
    "Second short label",
    "This is a medium length label",
    "This is also a medium length",
    "Now, this label is actually quite long, really long",
    "This label is also actually quite long, really long"
  ) %>% 
    fct_inorder %>% 
    fct_rev,
  facs = str_c(
    "facet", 1:3
  ) %>% 
    rep(each = 2),
  x = runif(6)
) |> 
  mutate(labs = str_pad(labs, max(str_width(labs)), side = "both"))

t1 %>% 
  ggplot(
    aes(
      x, labs
    )
  ) +
  geom_point() +
  facet_grid(
    vars(facs), 
    scales = "free_y"
  ) +
  labs(
    x = "",
    y = ""
  ) +
  theme(
    axis.text.y = element_text(hjust = .5)
  )