How to place circles around specific data points on a scatter plot in R?

Question

My question is two fold:

1) Is it possible to place a circle around specific data points on a scatter plot in R?
2) If so, how would I place separate circles of a defined radius around (5, 6) and (18, 23) given the following data.

x <- c(2, 5, 7, 9, 12, 16, 18, 21)
y <- c(3, 6, 10, 13, 15, 19, 23, 25)
plot(x, y)

(NB: This is not a request to colour specific data points on the plot, but to place a circle around them)

It's not clear if you mean one circle encompassing both points, or 2 circles - one around each point. — thelatemail
– thelatemail, Commented May 13, 2015 at 3:06
Thanks for asking for clarification. I mean separate circles (1 around each point) of a defined radius of the same size. — Alison Bennett
– Alison Bennett, Commented May 13, 2015 at 3:15
To me, defined radius =/= same radius, i.e. you can define different radius or the same radius. — user3710546
– user3710546, Commented May 13, 2015 at 3:20
Ah, thank-you again. I mean circles of the same radius which I have defined. — Alison Bennett
– Alison Bennett, Commented May 13, 2015 at 3:24

MrFlick · Accepted Answer · 2015-05-13 03:05:19Z

7

Check out the ?symbols help page for drawing circles

x <- c(2, 5, 7, 9, 12, 16, 18, 21)
y <- c(3, 6, 10, 13, 15, 19, 23, 25)
plot(x, y)
symbols(x=c(5,18), y=c(6,23), circles=rep(1,2), add=T, inches=F)

enter image description here

answered May 13, 2015 at 3:05

MrFlick

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Alison Bennett Over a year ago

Thanks @MrFlick. This is exactly what I was looking for. I also discovered the circles can be coloured by using symbols(x=c(5,18), y=c(6,23), circles=rep(1,2), add=T, inches=F, fg = "red")

Tad Dallas · Accepted Answer · 2015-05-13 03:05:33Z

5

You can use the symbols function in base R, where the size vector is the radius you want around each point.

x <- c(2, 5, 7, 9, 12, 16, 18, 21)
y <- c(3, 6, 10, 13, 15, 19, 23, 25)
plot(x, y)
size=runif(length(x))
symbols(x,y,circles=size)

answered May 13, 2015 at 3:05

Tad Dallas

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