From: <rory.winston_at_gmail.com>

Date: Thu, 03 Jul 2008 07:34:03 +0000

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Thu 03 Jul 2008 - 07:39:15 GMT

Date: Thu, 03 Jul 2008 07:34:03 +0000

Great! Thanks for the advice.

Cheers

Rory

------Original Message------

From: Duncan Murdoch

To: Rory Winston

Cc: r-help_at_r-project.org

Sent: 3 Jul 2008 05:08

Subject: Re: [R] Plotting Prediction Surface with persp()

On 02/07/2008 8:47 PM, Rory Winston wrote:

> Hi all

*>
**> I have a question about correct usage of persp(). I have a simple neural
**> net-based XOR example, as follows:
**>
**> library(nnet)
**> xor.data <- data.frame(cbind(expand.grid(c(0,1),c(0,1)), c(0,1,1,0)))
**> names(xor.data) <- c("x","y","o")
**> xor.nn <- nnet(o ~ x + y, data=xor.data, linout=FALSE, size=1)
**>
**> # Create an (x.y) surface and predict over all points
**> d <- data.frame(expand.grid(seq(0,1,.1), seq(0,1,.1)))
**> names(d) <- c("x","y")
**> p <- predict(xor.nn, d)
**> zmat <- as.matrix(cbind(d,p))
**>
**> Now my z matrix consists of x and y points, and the corresponding prediction
**> value for each (x,y) tuple. What would be the best way to plot these? I
**> tried persp(), but it didnt like the z matrix. Is there an alternative plot
**> function that I could use (I am presuming I need one of the 3d variants)?
*

You were close, but your zmat was constructed incorrectly. persp() wants a vector of values corresponding to its rows (e.g. x <- seq(0,1,.1)) and a vector of values corresponding to its columns (e.g. y <- seq(0,1,.1)), and it wants the z values in a matrix matching those.

So you need the lines I give above, then

dim(p) <- c(length(x),length(y))

persp(x,y,p)

You could also use persp3d() somewhat interchangeably (but it handles colour specs differently).

Duncan Murdoch

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