Extent of boundary of text in R plot [duplicate]

Answer 1

You can use strheight and strwidht to estimate that height and width of text.

Health warning: strheight and strwidth estimates text size in the current plot device. If you subsequently resize the plot, the R may resize the text automatically, but the rectangle will not resize. This is fine for interactive plots, but may cause problems when you save the plot to disk using png(); plot(...); dev.off()

x <- 1:300
y <- 1:300
plot(x, y, type="l")

txt <- "A note about this plot!"
rwidth <- strwidth(txt, font=2, cex=2)
rheight <- strheight(txt, font=2, cex=2)

tx <- 150
ty <- 100

text(tx, ty,txt, font=2, cex=2, col="blue", offset=1)

rect(tx-0.5*rwidth, ty-0.5*rheight, tx+0.5*rwidth, ty+0.5*rheight)

Answer 2

For maximum control, the grid package could also be used. In particular, grobs can be drawn at the time of rendering on the device, ensuring that resizing of the device is taken into account. The gridBase package provides functions to mix base and grid graphics.

An example with grid.table which has a drawDetails method,

 library(gridBase)
 library(gridExtra)

 par(oma=rep(1, 4), mfrow=c(1, 2), xpd=NA)
 plot(1:10, 1:10)
 vps <- baseViewports()
 pushViewport(vps$inner)
 pushViewport(vps$figure)
 pushViewport(vps$plot)
 ## grid.rect(gp=gpar(lwd=3, col="blue"))
 grid.table(expression("this is an expression"*integral(f(x)*dx, alpha, beta)),
            parse=TRUE, theme=theme.white(show.box=TRUE, separator = "red",
                          show.rownames = FALSE, show.colnames = FALSE))
 upViewport(0)

Answer 3

The plotrix package has a function textbox() that might be useful to you. Try something like this:

require(plotrix)
txt <- "Some notes about this plot"
plot(1:5)
textbox(x = c(1, 1 + 1.1*strwidth(txt)),
        y = 4,
        textlist = txt)