R Lapply PointsOnLines thru a list of psp objects - r

Question

Now that I have successfully, thanks to #Phil, coerced my SpatialLinesDataFrame into a list of list of psp objects, I need to use the SpatStat function pointsOnLines to create points along each list item(ie. Line), and have the marks of the line transferred to each set of points.
Im new to lapply, but seeing how it was used in converting the spatialdataframe to a list of psp objects, I think its appropriate to use it to apply the pointsOnLines function to each list? Alas, It isn't working for me. Help!
To continue the fylk example....
library("maptools")
library("rgdal")
library("spatstat")
base_dir <- system.file("shapes", package = "maptools")
fylk <- readOGR(base_dir, "fylk-val")
is(fylk)
out <- lapply(fylk#lines, function(i) { lapply(i#Lines, as.psp) })
out
dat <- fylk#data
for (i in seq_along(1:nrow(dat))) {
out[[i]] <- lapply(out[[i]], "marks<-", value = dat[i, , drop = FALSE])
}
for(i in seq_along(out)){
abc[[i]]<-(lapply(out[[i]],function(i){pointsOnLines(out[[i]],eps=10)}))
}
This doesnt work, and i can't troubleshoot why. I used [[]] as out is a list of lists?
Suggestions for the newbie?

Answer 1

Assuming the last lapply is your issue, consider a nested lapply to assign the result to abc:
abc <- lapply(out, function(o)
lapply(o, function(x) pointsOnLines(x, eps=10))
# EQUIVALENTLY:
# lapply(o, pointsOnLines, eps=10)
)
And to plot according to docs, run elementwise loop with Map (wrapper to mapply) between out and abc lists.
One psp and ppp pair:
plot(out[[1]], main="")
plot(abc[[1]], add=TRUE, pch="+")
Multiple psp and ppp pairs:
proc_plot <- function(X, Y) {
plot(X, main="")
plot(Y, add=TRUE, pch="+")
}
result <- Map(proc_plot, out, abc)