[R] Scatter plot - using colour to group points?

R. Michael Weylandt michael.weylandt at gmail.com
Mon Nov 21 21:32:06 CET 2011

I think the easiest way to do this is to set up a color vector with
ifelse and hand that off to the plot command: something like

col = ifelse(TEMP3[,"SITE"] == "BG1", "blue", "green") # Syntax is

For more complicated schemes, a set of nested ifelse()'s can get you
what you need. There are some other tricks with factors as well, but
they require a little more advanced use of R. Just for the record,
they'd look something like this:

X = letters[c(1,2,3,3,1,2,1,3,3,1,2,2,1)]

colX = c("red","green","blue")[as.factor(X)]

Hope this helps,

On Mon, Nov 21, 2011 at 2:17 PM, SarahH <sarah.g10 at hotmail.co.uk> wrote:
> Dear All,
> I am very new to R - trying to teach myself it for some MSc coursework.
> I am plotting temperature data for two different sites over the same time
> period which I have downloaded from a university weather station data
> archive.
> I am using the following code to create the plot
> plot ( x = TEMP3[,"TIME"], y = TEMP3[,"TEMP"], type = "p", col =
> TEMP3[,"SITE"], pch = 3, main = "Temperature changes", xlab = "Date", ylab =
> "Temberature[C]")
> I managed to use col = TEMP3["SITE"] to plot the two different sites( BG1
> and EA7) in different colours, but I am struggling to change the colours.
> I wanted to up a colour scheme to match the site, so tried
> BG1 <- "blue"
> EA7 <- "green"
> before the plot function, but the graphic just came out with red and black
> as before.
> There are other datasets in which there are more than two sites so I would
> really like to learn how to use colour to distinguish between them on a
> plot.
> Any direction would be very greatly received!
> Thank you very much
> Sarah
> --
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