[R] "cloud" function doesn't plot

[Tony Ross]

>From: "Simon Blomberg" <Simon.Blomberg at anu.edu.au>
>Date: Mon, 23 Jun 2003 16:26:39 +1000

>If you type ?cloud, you can see that you need to provide a formula as well 
>as a dataset. So if your variables are  x,y,z in dataframe dat, then 
>cloud(z~x*y, data=dat) should work.
[...]
>>is.matrix(sanity.MIF); is.numeric(sanity.MIF); dim(sanity.MIF); 
>>cloud(sanity.MIF)
>[1] TRUE
>[1] TRUE
>[1] 2970    3
>>

The "help(cloud)" facility states: "`formula' can be a matrix". As I stated, 
I have a 3-column numeric matrix, so colum 3 should be plotted as a point 
above the 1st and 2nd column co-ordinates.

No plot is produced however, just a blank graphics device.

Thanks.