3d scatterplot in R using rgl plot3d - different size for each data point?

Question

I am using

plot3d(x,y,z, col=test$color, size=4) 

to plot a 3d scatterplot of my dataset with R, but with rgl the size argument only takes one size.

Is it possible to have different sizes for each data point, perhaps with another library, or is there a simple workaround?

Thanks for your ideas!

Answer 1

Here's a work-around along the same lines suggested by Etienne. The key idea is to set up the plot, then use a separate call to points3d() to plot the points in each size class.

# Break data.frame into a list of data.frames, each to be plotted 
# with points of a different size
size <- as.numeric(cut(iris$Petal.Width, 7))
irisList <- split(iris, size)

# Setup the plot
with(iris, plot3d(Sepal.Length, Sepal.Width, Petal.Length, col=Species, size=0))

# Use a separate call to points3d() to plot points of each size
for(i in seq_along(irisList)) {
    with(irisList[[i]], points3d(Sepal.Length, Sepal.Width, 
                                 Petal.Length, col=Species, size=i))
}

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(FWIW, it does appear that there's no way to get plot3d() to do this directly. The problem is that plot3d() uses the helper function material3d() to set point sizes and as shown below, material3d() only wants to take a single numeric value.)

material3d(size = 1:7)
# Error in rgl.numeric(size) : size must be a single numeric value

Answer 2

Just in case anyone else stumbles across this years later, it is now completely possible to pass a variable into the size argument, e.g. with(test, plot3d(x,y,z, col=test$color, size=test$size)).

Actually, you can conduct operations on the data being fed to size and it will also work. I succeeded in making a basic size ratio with something along the lines of size = x/(max(x,na.rm=TRUE)-min(x,na.rm=TRUE)).

While it is true that material3d will only accept single numeric values, the expression or variable fed to size within the with statement should be evaluated beforehand, so material3d should still only see a single size value for each plotted point. Just a heads up since I spent a an hour or so fiddling with the workaround posted here before realizing it was unnecessary.