在 r ggplot 中，是否可以调整 x 轴上箱线图之间的间距？

Question

Say you want a simple boxplot, without any subgroups:

some_data %>%
        ggplot(aes(x=factor_1,
                   y=some_outcome)) + 
        geom_boxplot(width=0.2,notch = TRUE)

How do you adjust the space between the two boxes, without changing the box width ? So I just want to move the boxes closer or further away.

No online resourse seems to tackle this specific question. They either show how to change the box width, or they discuss the grouped boxplots that use the fill argument and how to adjust the spacing between the grouped boxes using position_dodge .

Thanks a lot!

Answer 1

You need to remember that you are drawing a plot into a plotting window with a fixed width. If you want the boxes to be closer together but remain the same size, and you don't want to change the size of the plotting window, then something needs to take up the extra space you have created. This can be achieved either by expanding the x-axis range of the plotting panel itself, or the margins around the plotting panel.

Let's start with a concrete example of data so we can run your code:

library(ggplot2)
library(dplyr)

set.seed(1)

some_data <- data.frame(factor_1 = c("0", "1"),
                        some_outcome = rnorm(200))

Now we can use your plotting code to get a reasonable replica of your plot:

some_data %>%
  ggplot(aes(x=factor_1,
             y=some_outcome)) + 
  geom_boxplot(width = 0.2, notch = TRUE)

Now, we can move the boxes closer together by expanding the x-axis range like this:

some_data %>%
  ggplot(aes(x=factor_1,
             y=some_outcome)) + 
  geom_boxplot(width = 0.67, notch = TRUE) +
  scale_x_discrete(expand = c(2, 2))

You can see that the extra space is taken up with some additional room in the panel on either side of the boxes.

An alternative is to make the panel narrower by increasing the margins around it, thereby allowing whitespace to take up the extra room:

some_data %>%
  ggplot(aes(x=factor_1,
             y=some_outcome)) + 
  geom_boxplot(width = 0.5, notch = TRUE) +
  theme(plot.margin = margin(10, 150, 10, 150))

I think the second option looks nicer. However, you would get a similar look if you just make your plotting window the correct size, then use your original plotting code (with appropriately selected width parameter)

# Drag plotting window to correct size, then run:

some_data %>%
  ggplot(aes(x=factor_1,
             y=some_outcome)) + 
  geom_boxplot(width = 0.4, notch = TRUE)