Text labels with background colour in R

Question

I was wondering if there is a simple way to add text labels with a contrasting background to an R plot using the base graphic system. Until now I have always used the rect() function together with graphics::strheight() and graphics::strwidth() to separately create the background box on which I then place my text using text():

# Prepare a noisy background:
plot(x = runif(1000), y = runif(1000), type = "p", pch = 16, col = "#40404050")

## Parameters for my text:
myText <- "some Text"
posCoordsVec <- c(0.5, 0.5)
cex <- 2

## Background rectangle: 
textHeight <- graphics::strheight(myText, cex = cex)
textWidth <- graphics::strwidth(myText, cex = cex)
pad <- textHeight*0.3
rect(xleft = posCoordsVec[1] - textWidth/2 - pad, 
        ybottom = posCoordsVec[2] - textHeight/2 - pad, 
        xright = posCoordsVec[1] + textWidth/2 + pad, 
        ytop = posCoordsVec[2] + textHeight/2 + pad,
        col = "lightblue", border = NA)

## Place text:
text(posCoordsVec[1], posCoordsVec[2], myText, cex = cex)

This is the result:

This does the job but it is quite tedious and you run into trouble when you start using pos, adj, offset etc. to tweak the positioning of the text. I am aware of TeachingDemos::shadowtext() to make text stand out from the background but this adds an outline instead of a box.

I am looking for a simple way to create text with a background box, something like text(x, y, labels, bg = "grey20"). I can't be the first person to require such a functionality and I am probably just missing something obvious. Help is appreciated. Thanks

user_9512084 · Answer

Quick hack using altcode character for a box:

plot(x=runif(1000), y=runif(1000), 
     type="p", pch=16, col="#40404050")

labels <- c("some text", "something else")

boxes <- sapply(nchar(labels), function(n) 
  paste(rep("\U2588", n), collapse=""))

pos <- rbind(c(0.2, .1), c(.5, .5))
text(pos, labels=boxes, col="#CCCCCC99")
text(pos, labels=labels, family = "mono")

user_10522567 · Answer

Bless your hardworking hearts, but plotrix has boxed.labels():

# Prepare a noisy background:
plot(x = runif(1000), y = runif(1000), type = "p", pch = 16, col = "#40404050")

## Parameters for my text:
myText <- "some Text"
posCoordsVec <- c(0.5, 0.5)
cex <- 2

## Background rectangle: 
textHeight <- graphics::strheight(myText, cex = cex)
textWidth <- graphics::strwidth(myText, cex = cex)
pad <- textHeight*0.3


## Place text:
plotrix::boxed.labels(posCoordsVec[1], posCoordsVec[2], myText, cex = cex, 
      border = NA, bg ="lightblue", xpad = 1.4, ypad = 1.4)

Text labels with background colour in R

4 Answers