出来画图，难免碰到个画箭头的需求。 简单，如下的代码就能安排。

set.seed(123)
d = data.frame(x=sample(1:10,8, replace = FALSE),
               y=sample(1:5,8,replace = T),
               vx=runif(8,2,4),
               vy=runif(8,1,3))
ggplot() + 
  geom_segment(data=d, mapping = aes(x=x, y=y, xend=x+vx, yend=y+vy), arrow = arrow(length=unit(0.2, "cm"))) + 
  ylim(0,10) + 
  theme_bw()

ggplot画箭头

画箭头时一些调整和参数设置，可以参考如下代码，看看箭头的头和尾的圆或者钝怎么设置。

df2 <- expand.grid(lineend=c('round',"butt","square"), 
                   linejoin=c("round","mitre","bevel"),
                   stringsAsFactors = FALSE)

df2 <- data.frame(df2, y=1:9)

ggplot(df2, aes(x=1,y=y,xend=2, yend=y+1, label=paste(lineend, linejoin))) + 
  geom_segment(lineend = df2$lineend, linejoin = df2$linejoin, size=3, arrow = arrow(length=unit(0.3, "inches"))) + 
  geom_text(hjust="outside", nudge_x = -0.2) + 
  xlim(0.5,2) 

更多画箭头的细节