R help - May 2008 - setting specific colours for different groups of points on a scatter plot

Hi,

I have a table with three columns of data, let's call these a, b and  
c. I have produced a scatter plot of a against b, but I would like to  
colour the points according to their corresponding c values. c takes  
the value of either 0,1,2,3 or 4 and so I would like to colour all of  
the points with a c value of 0 one colour, all those with a c value of  
1 another colour etc. When I use the following code, it colours the  
points using default colours, which are not suitable:

data<-read.table('abc',header=T, sep="\t")
attach(data)
library(lattice)
xyplot(a~b, col=c)

I was therefore wondering how to specify my own set of colours for  
each of the c values. Any help would really be appreciated as I have  
spent ages reading through the documentation, but with no luck.

Thanks,

Sarah

On 5/22/08, Sarah Kinnings <bssk at leeds.ac.uk>
wrote:
> Hi,
>
>  I have a table with three columns of data, let's call these a, b and
c. I
> have produced a scatter plot of a against b, but I would like to colour the
> points according to their corresponding c values. c takes the value of
> either 0,1,2,3 or 4 and so I would like to colour all of the points with a
c
> value of 0 one colour, all those with a c value of 1 another colour etc.
> When I use the following code, it colours the points using default colours,
> which are not suitable:
>
>  data<-read.table('abc',header=T, sep="\t")
>  attach(data)
>  library(lattice)
>  xyplot(a~b, col=c)
>
>  I was therefore wondering how to specify my own set of colours for each of
> the c values. Any help would really be appreciated as I have spent ages
> reading through the documentation, but with no luck.
The recommended way would be

mydata<-read.table('abc',header=T, sep="\t") # don't
attach
library(lattice)
xyplot(a~b, data = mydata, groups=c)

This would use the default lattice colors (which should be different
from the ones you saw). If you don't like them, you could specify your
own colors with

mycol <- c("blue", "red", "green",
"whatever")
xyplot(a~b, data = mydata, groups=c, col = mycol)

You will probably end up wanting a legend, in which case a better approach is

xyplot(a~b, data = mydata, groups=c,
       par.settings = simpleTheme(col = mycol),
       auto.key = TRUE)

-Deepayan