[R] R for-loop to add layer to lattice plot

[Deepayan Sarkar]

On Tue, Oct 27, 2020 at 6:04 PM Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
>
> Hello,
> I am using e1071 to run support vector machine. I would like to plot
> the data with lattice and specifically show the hyperplanes created by
> the system.
> I can store the hyperplane as a contour in an object, and I can plot
> one object at a time. Since there will be thousands of elements to
> plot, I can't manually add them one by one to the plot, so I tried to
> loop into them, but only the last is added.
> Here it the working example for more clarity:
>
> ```
> library(e1071)
> library(lattice)
> library(latticeExtra)
>
> make.grid <- function(x, n = 1000) {
>   grange = apply(x, 2, range)
>   x1 = seq(from = grange[1,1], to = grange[2,1], length = n)
>   x2 = seq(from = grange[1,2], to = grange[2,2], length = n)
>   expand.grid(X1 = x1, X2 = x2)
> }
>
> plot_list <- list()
> for (i in 1:10) {
>   x1 = rnorm(100, mean = 0.2, sd = 0.15)
>   y1 = rnorm(100, mean = 0.7, sd = 0.15)
>   y2 = rnorm(100, mean = 0.2, sd = 0.15)
>   x2 = rnorm(100, mean = 0.75, sd = 0.15)
>   df = data.frame(x = c(x1,x2), y=c(y1,y2),
>                   z=c(rep(0, length(x1)), rep(1, length(x2))))
>   df$z = factor(c(rep(0, length(x1)), rep(1, length(x2))))
>   df[, "train"] <- ifelse(runif(nrow(df)) < 0.8, 1, 0)
>   trainset <- df[df$train == 1, ]
>   testset <- df[df$train == 0, ]
>   trainColNum <- grep("train", names(df))
>   trainset <- trainset[, -trainColNum]
>   testset <- testset[, -trainColNum]
>   svm_model <- svm(z ~ .,
>                   data = trainset,
>                   type = "C-classification",
>                   kernel = "linear",
>                   scale = FALSE)
>   # generate contour
>   xmat = make.grid(matrix(c(testset$x, testset$y),
>                           ncol = 2, byrow=FALSE))
>   xgrid = as.data.frame(xmat)
>   names(xgrid) = c("x", "y")
>   z = predict(svm_model, xgrid)
>   xyz_dat = as.data.frame(cbind(xgrid, z))
>   plot_list[[i]] = contourplot(z ~ y+x, data=xyz_dat, pretty = TRUE,
>                                xlim=c(-1,50), ylim=c(-0.001, 0.05),
>                                labels = FALSE, col = "blue", lwd = 0.5)
>
> }
> # the contour is stored in the object plot_list
> str(plot_list) # confirm that there is data here
>
> # I can add one element at the time to lattice's xyplot and store it
> in an object P
> P = xyplot(y ~ x, group = z, data = df,
>            pch = 16, cex = 1.5, alpha = 0.25) + as.layer(plot_list[[1]]) +
>   as.layer(plot_list[[2]])
> plot(P)  # this demonstrates that the lines are not the same
>
> # but if I add the elements via loop, it does not work
> for (i in 1:length(plot_list)) {
>   print(i)
>   P = xyplot(y ~ x, group = z, data = df,
>              pch = 16, cex = 1.5, alpha = 0.25) + as.layer(plot_list[[i]])
> }
> plot(P)
> ```
>
> Am I missing something?

Yes, as Mark says, you need to change the last part to something like

P = xyplot(y ~ x, group = z, data = df, pch = 16, cex = 1.5, alpha = 0.25)
for (i in 1:length(plot_list)) {
  print(i)
  P = P + as.layer(plot_list[[i]])
}
plot(P)

-Deepayan

> Thank you
>
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