R 将箭头绘制在图形外部，而不是图形内部

发布于02月24日

我正试着把箭头画在图的外面.我try 了许多不同的选项，但他们一直在图中绘制箭头.有没有办法把它画在边界框之外？

set.seed(57)
discharge <- data.frame(date = seq(as.Date("2011-01-01"), as.Date("2011-12-31"), by="days"),
discharge = rexp(365))

test <- ggplot(discharge) +
geom_line(aes(x = date, y = discharge)) +
geom_hline(yintercept = 5.5, linetype= "dashed", color = "red") + 
geom_text(aes(x = date[13], y = 5.5, label = "High"))

(test + annotate(geom = "segment", x = as.Date("2011-01-01"), 
              y = -1, xend = as.Date("2011-01-01"), yend = 0, 
              arrow = arrow(length = unit(3, "mm")), color = "red"))

推荐答案

ggplot2 >= 3.5.0(！)引入的一项很好的功能是，现在可以将注释作为数字放置在打印面板的相对单位中(请参见here).为此，我们必须将annotate内的位置包装为I().这样做的好处是，添加注释不会影响比例范围.

此外，像往常一样，我们必须在coord_cartesian中设置clip="off"，并在绘图面板外腾出一些空间，例如通孔plot.margin.

set.seed(57)
discharge <- data.frame(
  date = seq(as.Date("2011-01-01"), as.Date("2011-12-31"), by = "days"),
  discharge = rexp(365)
)

library(ggplot2)

packageVersion("ggplot2")
#> [1] '3.5.0'

test <- ggplot(discharge) +
  geom_line(aes(x = date, y = discharge)) +
  geom_hline(yintercept = 5.5, linetype = "dashed", color = "red") +
  geom_text(data = ~.x[13, , drop = FALSE], aes(x = date, y = 5.5, label = "High"))

test + 
  annotate(
    geom = "segment", x = as.Date("2011-01-01"),
    y = I(-.125), xend = as.Date("2011-01-01"), yend = I(-.05),
    arrow = arrow(length = unit(3, "mm")), color = "red"
  ) +
  coord_cartesian(clip = "off") +
  theme(plot.margin = margin(5.5, 5.5, 22, 5.5))