Constructing a bubble trellis plot with lattice in R - data-visualization

Question

First off, this is a homework question. The problem is ex. 2.6 from pg.26 of An Introduction to Applied Multivariate Analysis. It's laid out as:
Construct a bubble plot of the earthquake data using latitude and longitude as the scatterplot and depth as the circles, with greater depths giving smaller circles. In addition, divide the magnitudes into three equal ranges and label the points in your bubble plot with a different symbol depending on the magnitude group into which the point falls.
I have figured out that symbols, which is in base graphics does not work well with lattice. Also, I haven't figured out if lattice has the functionality to change symbol size (i.e. bubble size). I bought the lattice book in a fit of desperation last night, and as I see in some of the examples, it is possible to symbol color and shape for each "cut" or panel. I am then working under the assumption that symbol size could then also be manipulated, but I haven't been able to figure out how.
My code looks like:
plot(xyplot(lat ~ long | cut(mag, 3), data=quakes,
layout=c(3,1), xlab="Longitude", ylab="Latitude",
panel = function(x,y){
grid.circle(x,y,r=sqrt(quakes$depth),draw=TRUE)
}
))
Where I attempt to use the grid package to draw the circles, but when this executes, I just get a blank plot. Could anyone please point me in the right direction? I would be very grateful!

Answer 1

Here is the some code for creating the plot that you need without using the lattice package. I obviously had to generate my own fake data so you can disregard all of that stuff and go straight to the plotting commands if you want.
####################################################################
#Pseudo Data
n = 20
latitude = sample(1:100,n)
longitude = sample(1:100,n)
depth = runif(n,0,.5)
magnitude = sample(1:100,n)
groups = rep(NA,n)
for(i in 1:n){
if(magnitude[i] <= 33){
groups[i] = 1
}else if (magnitude[i] > 33 & magnitude[i] <=66){
groups[i] = 2
}else{
groups[i] = 3
}
}
####################################################################
#The actual code for generating the plot
plot(latitude[groups==1],longitude[groups==1],col="blue",pch=19,ylim=c(0,100),xlim=c(0,100),
xlab="Latitude",ylab="Longitude")
points(latitude[groups==2],longitude[groups==2],col="red",pch=15)
points(latitude[groups==3],longitude[groups==3],col="green",pch=17)
points(latitude[groups==1],longitude[groups==1],col="blue",cex=1/depth[groups==1])
points(latitude[groups==2],longitude[groups==2],col="red",cex=1/depth[groups==2])
points(latitude[groups==3],longitude[groups==3],col="green",cex=1/depth[groups==3])

Answer 2

You just need to add default.units = "native" to grid.circle()
plot(xyplot(lat ~ long | cut(mag, 3), data=quakes,
layout=c(3,1), xlab="Longitude", ylab="Latitude",
panel = function(x,y){
grid.circle(x,y,r=sqrt(quakes$depth),draw=TRUE, default.units = "native")
}
))
Obviously you need to tinker with some of the settings to get what you want.

Answer 3

I have written a package called tactile that adds a function for producing bubbleplots using lattice.
tactile::bubbleplot(depth ~ lat*long | cut(mag, 3), data=quakes,
layout=c(3,1), xlab="Longitude", ylab="Latitude")