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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