R help - May 2009 - wireframe 3-D problems

Dear All R Users,

I am trying to graph a 3-D graph of simulated data for logit models using
the powerful wireframe command, but I got stuck. Here are the codes:

x <- seq(-4, 4, by=0.01)
 y <- seq(-4, 4, by=0.01)
 p <- 1/(1+exp(-0.12*x + 0.35*y))
 mydata <- cbind(x, y, p)
 require(lattice)
 wireframe(p~x*y, data=mydata)

 and I received the following message:

Error in eval(substitute(groups), data, environment(formula)) :
  numeric 'envir' arg not of length one

Can anyone here point me to the right direction? Thanks!

Jun Xu, PhD
Assistant Professor
Department of Sociology
Ball State University

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Xu Jun wrote:
> 
> I am trying to graph a 3-D graph of simulated data for logit models using
> the powerful wireframe command, but I got stuck. Here are the codes:
> 
> x <- seq(-4, 4, by=0.01)
>  y <- seq(-4, 4, by=0.01)
>  p <- 1/(1+exp(-0.12*x + 0.35*y))
>  mydata <- cbind(x, y, p)
>  require(lattice)
>  wireframe(p~x*y, data=mydata)
> 
>  and I received the following message:
> 
> Error in eval(substitute(groups), data, environment(formula)) :
>   numeric 'envir' arg not of length one
> 
> Can anyone here point me to the right direction? Thanks!
> 
> 
Your x and y variables were only evaluated along a single line,
not over the entire grid (other solutions are possible using
outer() and rep() ...)

x <- seq(-4, 4, by=0.25)
y <- seq(-4, 4, by=0.25)
mydata <- expand.grid(x=x,y=y)
p <- 1/(1+exp(-0.12*mydata$x + 0.35*mydata$y))
mydata <- data.frame(x=mydata$x,y=mydata$y,p)
require(lattice)
wireframe(p~x*y, data=mydata)
## should play with "screen" argument, see ?panel.wireframe

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Ben,

Thank you for your help!

Jun

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