Callout text in R

Question

I want add callout text to my R-plot. For example, I have some plot:

x <- seq(0, 2, by=0.1)
y <- x*x
plot(x, y, type="l")

I want to add some callout text like this:

There are some standard methods for it?

Answer 1

Have a look at ?text (and ?arrows).

x <- seq(0, 2, by=0.1)
y <- x*x
plot(x, y, type="l")

text(0.25, 2, "Some text", pos=3)
arrows(0.25, 2, 1, 1)

UPDATE:

You could combine text, lines and arrows into a small function:

x <- seq(0, 2, by=0.1)
y <- x*x
plot(x, y, type="l")

# x0, y0: coordinates of text; see ?text
# x1, y1: coordinates to which the arrows are drawn; see ?arrows
# labels: text
# vOffset/hOffset: vertical/horizontal offset
callout <- function(x0, y0, x1, y1, labels, vOffset=0.25, hOffset=0.25) {
  ## fetch labels width/height
  w <- strwidth(labels)
  w2 <- w/2
  h <- strheight(labels)
  h2 <- h/2

  ## draw text
  text(x0, y0, labels=labels)

  ## calulate arrow starting point/line end point
  x01 <- x0+w2*(1+hOffset)
  y01 <- y0-h2*(1+vOffset)

  ## draw horizontal lines
  for (i in seq(along=x0)) {
    lines(c(x0[i]-w2[i], x01[i]), c(y01[i], y01[i]))
  }

  ## draw arrows
  arrows(x0=x01, y0=y01, x1=x1, y1=y1)
}

callout(c(0.25, 0.25), c(2, 3), c(1, 1.5), c(1, 2.25),
        c("Some text", "Some other text"))