r - cowplot:如何通过修改轴限制来自定义主面板和边缘图之间的间隙？

Question

这是关于@ClausWilke ( see post ) 提供的解决方案之一的后续问题，用于在主面板和边际图之间插入间隙。如何决定 (scale_x_continuous) 限制？另外，如果我们使用“NA”作为上限会怎样？

# Example with limits set to: (-2,4.5)
require(ggplot2)
require(cowplot)

pmain <- ggplot(data = mpg, aes(x = cty, y = hwy)) + 
  geom_point() + 
  xlab("City driving (miles/gallon)") +
  ylab("Highway driving (miles/gallon)") + 
  theme_grey()

xbox2 <- axis_canvas(pmain, axis = "x", coord_flip = TRUE) + 
  geom_boxplot(data = mpg, aes(y = cty, x = 1))  + 
  scale_x_continuous(limits = c(-2, 4.5)) + coord_flip()

ybox2 <- axis_canvas(pmain, axis = "y") + 
  geom_boxplot(data = mpg, aes(y = hwy, x = 1)) + 
  scale_x_continuous(limits = c(-2, 4.5))

p1 <- insert_xaxis_grob(pmain, xbox2, grid::unit(0.8, "in"), position = "top")
p2 <- insert_yaxis_grob(p1, ybox2, grid::unit(0.8, "in"), position = "right")

ggdraw(p2)

Answer 1

有了连续的 x 轴刻度，您可以使用 expand_limits 在主图和边缘图之间添加一些空白空间。

例如，您的 ybox2 是一个具有连续 x 轴刻度的单箱线图。默认情况下，该图的 x 范围大约为 0.6 到 1.4(您可以通过运行 ggplot(mpg, aes(y=hwy, x=1)) + geom_boxplot() 来查看)。以下代码将 x 轴下限设置为 0.2，这意味着大约 0.4/(0.8+0.4) = 33% 的 x 轴范围将是主图和边际图之间的边距。我们为 xbox2 做同样的事情。

ybox2 <- axis_canvas(pmain, axis = "y") + 
  geom_boxplot(data = mpg, aes(y = hwy, x = 1)) +
  expand_limits(x = 0.2)

xbox2 <- axis_canvas(pmain, axis = "x", coord_flip = TRUE) + 
  geom_boxplot(data = mpg, aes(y = cty, x = 1))  + 
  coord_flip() +
  expand_limits(x = 0.2)

p1 <- insert_xaxis_grob(pmain, xbox2, grid::unit(0.4, "in"), position = "top")
p2 <- insert_yaxis_grob(p1, ybox2, grid::unit(0.4, "in"), position = "right")

ggdraw(p2)