R help - Oct 2009 - How to plot multiple data sets with different colors (also with legend)?

The following commands only show the data in 'y'. I'm wondering how
to
show the data in 'x' as well. I also want to add a legend to show that
blue points corresponds to 'x' and yellow points correspond to
'y'.
Could somebody let me know what the correct commands should be?

x=rbind(c(10,11),c(10,11))
y=cbind(-1:0,-1:0)
plot(y,col='yellow')
points(x,col='blue')

Hi, 

the blue point is not shown simply because it is printed outside 
the current plot area. If you want to use the base graphics, you 
have to manually define the xlim and ylim of the plot. Legend is added 
with the command "legend". 

E.g.
x=rbind(c(10,11),c(10,11))
y=cbind(-1:0,-1:0)
plot(y,col='yellow', xlim=c(-1,11), ylim=c(-1,11))
points(x,col='blue')
legend("topleft", c("x","y"),
col=c('blue', 'yellow'), pch=1)

This is nevertheless most easily done in ggplot2. 
E.g.
library(ggplot2)
# put the whole data in a data frame
# and add a new variable to distinguish both
dat <- data.frame(rbind(x,y), var=rep(c('x','y'), each=2))
qplot(x=X1,y=X2, colour=var, data=dat)


HTH, 

Matthieu

On 10/19/2009 07:37 AM, Peng Yu wrote:
> The following commands only show the data in 'y'. I'm wondering
how to
> show the data in 'x' as well. I also want to add a legend to show
that
> blue points corresponds to 'x' and yellow points correspond to
'y'.
> Could somebody let me know what the correct commands should be?
>
> x=rbind(c(10,11),c(10,11))
> y=cbind(-1:0,-1:0)
> plot(y,col='yellow')
> points(x,col='blue')
>
>    
Hi Peng,
To show the "x" points, you will have to set both the xlim and ylim 
arguments:

plot(y,col="yellow",xlim=c(-1,11),ylim=c(-1,11))
points(x,col="blue")

I'm not sure why you are passing the points as matrices, but this means 
that the "x" points are the same.

Jim