how-to-draw-lines-outside-of-plot-area-in-ggplot2 (opens new window)

想要在ggplot2绘图区域外添加额外的图形元素，可以使用grid绘图系统提供的图层元素。 另外，ggplot2默认只展示绘图区域内的图形，越界的图层元素会被剪切掉。可以通过笛卡尔坐标函数修改clip参数。 关闭clip之后，它允许在绘图上的任何位置 (包括在绘图边距中) 绘制数据点。

需要注意的是，如果通过xlim和ylim设置了限制，并且某些数据点超出了这些限制，则这些数据点也可能会显示在轴，图例，绘图标题或绘图边距等位置。

# clip 默认为开启状态
coord_cartesian(clip = 'off')

下面例子显示在ggplot2绘图区域外添加文字和线条注释

library (ggplot2)
library(grid)

test= data.frame(
  group=c(rep(1,6), rep(2,6)),
  subgroup=c( 1,1,1,2,2,2,1,1,1,2,2,2),
  category=c( rep(1:3, 4)),
  count=c( 10,80,10,5,90,5,  10,80,10,5,90,5   )
)

p <- ggplot(test, aes(x = subgroup, y = count, fill = category)) + 
    geom_bar(stat = "identity") + 
    facet_grid(.~ group) +
  ## 关闭自动剪裁，这个很重要，不然看不见图
    coord_cartesian(clip = 'off') +
    theme(legend.position="none",  plot.margin = unit(c(0,9,2,0), "lines"))


# Create the text Grobs
Text1 = textGrob("Text 1")
Text2 = textGrob("Text 2")
Text4 = textGrob("Text 4")

# Draw the plot
# Text 1
p1 = p + annotation_custom(grob = Text1,  xmin = 3., xmax = 3., ymin = 85, ymax = 100) +
  annotation_custom(grob = linesGrob(), xmin = 2.6, xmax = 2.75, ymin = 100, ymax = 100) +
  annotation_custom(grob = linesGrob(), xmin = 2.6, xmax = 2.75, ymin = 85, ymax = 85) +
  annotation_custom(grob = linesGrob(), xmin = 2.75, xmax = 2.75, ymin = 85, ymax = 100)

# Text 2
p1 = p1 + annotation_custom(grob = Text2,  xmin = 3, xmax = 3, ymin = 20, ymax = 80) +
  annotation_custom(grob = linesGrob(), xmin = 2.6, xmax = 2.75, ymin = 80, ymax = 80) +
  annotation_custom(grob = linesGrob(), xmin = 2.6, xmax = 2.75, ymin = 20, ymax = 20) +
  annotation_custom(grob = linesGrob(), xmin = 2.75, xmax = 2.75, ymin = 20, ymax = 80)

# Text 4
p1 = p1 + annotation_custom(grob = Text4,  xmin = 3, xmax = 3, ymin = 0, ymax = 15) +
  annotation_custom(grob = linesGrob(), xmin = 2.6, xmax = 2.75, ymin = 15, ymax = 15) +
  annotation_custom(grob = linesGrob(), xmin = 2.6, xmax = 2.75, ymin = 0, ymax = 0) +
  annotation_custom(grob = linesGrob(), xmin = 2.75, xmax = 2.75, ymin = 0, ymax = 15)

p1