A fast method to add annotations to a plot

March 28, 2017
By

(This article was first published on Bluecology blog, and kindly contributed to R-bloggers)

A fast method to add annotations to a plot

Making professional looking plots in R can be fiddly. One task that I often spend ages doing is manually finding coordinates to add labels.
Wouldn’t it be nice if you could just send the coordinates directly to your text editor?

I did some searching and found on stackoverflow that you can send R objects to the clipboard. So here is my solution using that trick.

Adding text to the right position on a plot can be a real hassle. Here I show how to use a simple function to click on a figurea and put coordinates onto your clipboard.

You can get R to send data directly to the clipboard using the pipe command. Below is a little function I wrote that takes coordinates from locator() and sends them to your clipboard. Then you can just hit cmd-v to paste them into your text editor (nb I understand this may need some slight modifications to work on linux or windows, I use OSX):

loccopy <- function(n, digits = 2){
    data <- locator(n)
    data <- round(cbind(data$x, data$y), digits)
    clip <- pipe("pbcopy", "w")
    write.table(data, file = clip, col.names = F, row.names = F)
    close(clip)
}

Let’s test it out:

set.seed(42)
plot(runif(100))
loccopy(1)

Now hit cmd-v (or equivalent on your OS).

69.23 0.84

Let’s add a label using our fast method for coordinates:

text(69.23, 0.84, "Unusual data point", pos =4, offset = 0)

The pos=4 and offset=0 ensures that the text goes directly to the right of our coordinates.

That’s it. Hope it helps speed up your workflow.

To leave a comment for the author, please follow the link and comment on their blog: Bluecology blog.

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