How to label ticks names for only specific ticks in ggplot2?

Question

Is there a faster/easier way to display only specific y-axis tick labels like I have done here:

In the code you can see that I manually add/edit the break names to achieve this result.

Thank you in advance for taking the time to help me resolve this issue.

library(tidyverse)
library(reshape2)

green <- c(6.95, 7.21, 6.98, 7.08, 7.06, 
7.33, 7.12, 6.97, 7.03, 7.05, 6.83, 6.94, 
6.96, 6.98, 7.21, 7.04, 6.92, 7.04, 7.15, 
7.10, 7.01, 6.86)
purple <- c(5.70, 5.80, 5.93, 5.33, 5.32, 
5.68, 4.76, 4.93, 5.13, 5.78, 5.66, 5.85, 
5.92, 5.61, 5.91, 7.16, 5.78, 5.98, 5.92, 
6.01, 6.14, 5.90)
red <- c(5.85, 6.04, 5.91, 5.77, 5.61, 
5.93, 5.73, 5.36, 5.52, 5.38, 5.40, 5.51, 
5.70, 5.33, 5.84, 7.22, 5.55, 5.70, 5.59, 
5.66, 5.74, 5.71)

d_long2 <- data.frame(green, purple, red)
d_long2 <- melt(d_long2)

ggplot(d_long2, aes(x = variable, y = value, colour = variable)) +
geom_boxplot(show.legend = FALSE) +
theme_classic() + 
scale_x_discrete(name = " ",
               labels = c("Control", 
                          "Aluminium Poor pH 5.8", 
                          "Aluminium Rich pH 5.8"),
               expand = c(0.15, 0.15)
) +
scale_y_continuous(name = "pH",
                 breaks = seq(4.7, 7.4, by = 0.1),  
                 labels = c(" ", " ", " ", "5", 
                            " ", " ", " ", " ", "5.5", 
                            " ", " ", " ", " ", "6", 
                            " ", " ", " ", " ",  "6.5 ", 
                            " ", " ", " ", " ","7", 
                            " ", " ", " ", "7.4")) +
scale_colour_manual(values = c("#00CC00", 
                             "#9966FF", 
                             "#FF0000"))

Jon Spring · Answer 1 · 2022-06-21T17:30:33.573

Here's a general solution that will work for any range, creating ticks every 0.1 and labels every 0.5.

I like scales::breaks_width for specifying the frequency of breaks, then we could use a formula to specify we only want the ticks that are approximately* 0.5 to have labels.

  scale_y_continuous(name = "pH",
                     breaks = scales::breaks_width(0.1),
                     labels =  ~if_else(near(.x %% 0.5, 0), as.character(.x), "")) +

I used if_else here, which is tidyverse's pickier version of base ifelse; it requires the TRUE and FALSE both be the same data type, so here I format the TRUE value as character.

* We have to say "approximately" because computers store decimals as floating point numbers in base 2, which in many cases can't exactly match our base-10 decimals. Why are these numbers not equal?

score 1 · Accepted Answer · answered Jun 21 '22 at 17:20

With very specific values like this you are going to have to specify them somehow, but you can do this without all the empty strings by using ifelse

ggplot(d_long2, aes(x = variable, y = value, colour = variable)) +
geom_boxplot(show.legend = FALSE) +
theme_classic() + 
scale_x_discrete(name = " ",
               labels = c("Control", 
                          "Aluminium Poor pH 5.8", 
                          "Aluminium Rich pH 5.8"),
               expand = c(0.15, 0.15)
) +
scale_y_continuous(name = "pH",
                 breaks = seq(4.7, 7.4, by = 0.1),  
                 labels = ~ifelse(.x %in% c(5, 5.5, 6, 6.5, 7, 7.4), .x, "")) +
scale_colour_manual(values = c("#00CC00", 
                             "#9966FF", 
                             "#FF0000"))

tjebo · Answer 3 · 2022-06-21T21:59:55.443

This is essentially a duplicate to Adding minor tick marks to the x axis in ggplot2 (with no labels)

You can use the ggh4x package. Advantages:

There will be no labels drawn, not even ""
you can define the length of the minor ticks
no need for any indirect labelling using ifelse or similar

library(ggh4x)
#> Loading required package: ggplot2

ggplot(d_long2, aes(x = variable, y = value, colour = variable)) +
  geom_boxplot(show.legend = FALSE) +
  theme_classic() +
  scale_x_discrete(
    name = " ", labels = c("Control", "Aluminium Poor pH 5.8", "Aluminium Rich pH 5.8"),
    expand = c(0.15, 0.15)
  ) +
  scale_y_continuous(
    minor_breaks = seq(4.7, 7.4, by = 0.1),
    breaks = c(5, 5.5, 6, 6.5, 7, 7.4),
    guide = "axis_minor"
  ) +
  scale_colour_manual(values = c(
    "#00CC00",
    "#9966FF",
    "#FF0000"
  )) +
  ## setting the minor ticks to the same length
  theme(ggh4x.axis.ticks.length.minor = rel(1))

How to label ticks names for only specific ticks in ggplot2?

3 Answers3

Linked