How to add arrow using grid

Question

I want to add an arrow using a package gridthat will highlight an important part of my chart. I want the arrow to look like the image on the right side.

On the left side is my chart, created by the code below, and on the right is my chart with an arrow (I added it with Paint). It is my goal.

library(grid)
library(lattice)
library(sandwich)

data("Investment")
Investment <- as.data.frame(Investment)

pushViewport(plotViewport(c(5, 4, 2, 2)))
pushViewport(dataViewport(Investment$Investment, 
                      Investment$GNP,
                      name="Zaleznosc Investment od GNP"))

grid.points(Investment$Investment, Investment$GNP, gp=gpar(cex=0.5))

grid.rect()
grid.xaxis()
grid.yaxis()
grid.text("Investment", y=unit(-3, "line"))
grid.text("GNP", x=unit(-3, "line"), rot=90)
popViewport()

Answer 1

You can use the code that you have, but up to popViewport()add the code to add an arrow.

grid.lines(x = unit(c(0.42, 0.74), "npc"),
          y = unit(c(0.8, 0.86), "npc"),
        gp = gpar(fill="black"),
          arrow = arrow(length = unit(0.2, "inches"), 
            ends="last", type="closed"))

Also, tracking @alistaire grid graphics is a little tricky to track. What you are trying to do is basically simple in the base schedule.

plot(GNP ~ Investment, data=Investment)
arrows(250, 2600, 380, 2750, code = 2, lwd=2)

, , . arrows . , shape .

library(shape)
plot(GNP ~ Investment, data=Investment)
Arrows(250, 2600, 380, 2750, code = 2, 
    arr.type="triangle", arr.width=0.4)

Answer 2

, @alistaire ggplot2 grid .

, ggplot2, annotate() .

data(Investment, package = "sandwich")

library(ggplot2)
ggplot(as.data.frame(Investment)) +
  aes(Investment, GNP) +
  geom_point(shape = 1L) +
  theme_bw() +
  annotate("segment", x = 250, xend = 380, y = 2600, yend = 2800, 
           arrow = arrow(length = unit(0.2, "inches"), ends = "last", type = "closed"))

, ggplot2 arrow() grid.