On 05/12/2013 10:33 AM, Jun Shen wrote:
Hi Federico/Duncan/David/Bert,
Thank you for your thoughtful comments and it's a great learning
experience. I can see the critical point here is to find a right function
to make the prediction. So I was thinking to start with "loess". However
the predict.loess gave me an error as follows
Error in `$<-.data.frame`(`*tmp*`, "z", value = c(0.417071766265867,
0.433916401753023, :
replacement has 20 rows, data has 400
Here is the code I tried. Thank you for your help again!
Jun
=====================================
x<-runif(20)
y<-runif(20)
z<-runif(20)
library(rgl)
plot3d(x,y,z)
loess(z~x+y,control=loess.control(surface='direct'),span=.5,degree=2)->fit.loess
xnew <- seq(min(x), max(x), len=20)
ynew <- seq(min(y), max(y), len=20)
df <- expand.grid(x = xnew, y = ynew)
df$z<-predict(fit.loess,newdata=df)
After the error, use traceback() to find which function called
`$<-.data.frame`. It shows that it was your final assignment
df$z<-predict(fit.loess,newdata=df)
which causes the error, because the predict function returns a matrix.
So you can get the plot using
surface3d(xnew, ynew, predict(fit.loess,newdata=df), col="gray")
You may want
aspect3d(1,1,1)
afterwards; loess isn't so good at extrapolation. Or you may want to
set predictions to NA outside the convex hull of your data. (I'm not
sure which function is easiest to calculate that, but here's one way:
hullx <- x[chull(x,y)]
hully <- y[chull(x,y)]
keep <- sp::point.in.polygon(df$x, df$y, hullx, hully)
znew <- predict(fit.loess,newdata=df)
znew[!keep] <- NA
plot3d(x,y,z)
surface3d(xnew, ynew, znew, col="gray")
aspect3d(1,1,1)
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