[R-sig-Geo] Help with as.numeric(rownames(over(SpatialPoints(set1, set2, returnList= TRUE)[[1]]))
Alan Briggs
awbriggs at gmail.com
Sun Nov 1 19:35:30 CET 2015
Hello.
Below is a fully repeatable R-Script that I'm having trouble with.
Generally, here's what I'm trying to do:
1) Randomly generate a tile.list()
2) Randomly generate a new point
3) Identify which polygon in the tile.list the new randomly generated point
is in
This works fine MOST of the time. However, occasionally, I get an error
returned:
Error in `[<-.data.frame`(`*tmp*`, list, 3, value = numeric(0)) :
> replacement has length zero
While troubleshooting, I realized I get numeric(0) returned for certain
sets of new random points when I run the command
as.numeric(rownames(over(SpatialPoints(walker[i,1:2]),vpl,returnList=
TRUE)[[1]])). I thought maybe this was a boundary issue, but the points
don't lie on the edge, nor are they the centroid.
Any help you can provide would be greatly appreciated!
Regards,
Alan
R-Script Below:
### Help Question for r-sig-geo ###
> rm(list = ls())
> library(deldir)
> library(sp)
> library(plyr)
> side_length = 100
> ## Create random SET of XY coordinates (size = 100x100)
> set.seed(11)
> df = data.frame(matrix(sample(1:100,16,replace=TRUE),nrow=8))
> ## Convert df to SPatialPointsDataFrame
> spdf <- SpatialPointsDataFrame(df,df)
> ## deldir() function creates tesselation (voronoi) plot
> z <- deldir(df,plotit=TRUE,wl='te')
> ## tile.list() creates a list of data for tiles
> zz <- tile.list(deldir(df,plotit=TRUE,wl='te'))
> ## Voronoi Polygons Function
> voronoipolygons = function(layer) {
> require(deldir)
> crds = layer at coords
> z = deldir(crds[,1], crds[,2])
> w = tile.list(z)
> polys = vector(mode='list', length=length(w))
> require(sp)
> for (i in seq(along=polys)) {
> pcrds = cbind(w[[i]]$x, w[[i]]$y)
> pcrds = rbind(pcrds, pcrds[1,])
> polys[[i]] = Polygons(list(Polygon(pcrds)), ID=as.character(i))
> }
> SP = SpatialPolygons(polys)
> voronoi = SpatialPolygonsDataFrame(SP, data=data.frame(x=crds[,1],
> y=crds[,2], row.names=sapply(slot(SP, 'polygons'),
> function(x) slot(x, 'ID'))))
> }
> ## Generate SpatialPolygonsDataFrame to use as input for over() function
> vpl <- voronoipolygons(spdf)
> ## Random Walk Function generates North, South East or West movement
> ## with transit from across screen (like PacMan, going out one side,
> ## coming back on the other side) to prevent getting stuck in corner
> random_walk <- function(step_quantity, step_length, plot = FALSE){
> require(ggplot2)
>
> walker <- data.frame(matrix(c(0,0), nrow = step_quantity, ncol = 3,
> byrow = T))
> names(walker)[1]<-paste("x")
> names(walker)[2]<-paste("y")
> names(walker)[3]<-paste("which")
>
> ## Seed random initial starting point
> walker[1,1:2] <- matrix(sample(1:100,2,replace=TRUE),nrow=1)
> walker[1,3] <-
> as.numeric(rownames(over(SpatialPoints(walker[1,1:2]),vpl,returnList=
> TRUE)[[1]]))
>
> where_to <- as.numeric()
>
> for(i in 2:step_quantity){
> where_to <- as.numeric()
> where_to <- walker[i-1,1:2]
> which_next <- sample(c("bb","dd","ff","hh"),1)
>
> if (which_next == "bb") {
> if (walker[i-1,2] == side_length) {where_to[1,2] <- 0
> } else {where_to[1,2] <- walker[i-1,2]+step_length}
> }
>
> else if (which_next == "dd") {
> if (walker[i-1,1] == 0 ) {where_to[1,1] <- side_length
> } else {where_to[1,1] <- walker[i-1,1]-step_length}
> }
>
> else if (which_next == "ff") {
> if (walker[i-1,1] == side_length) {where_to[1,1] <- 0
> } else {where_to[1,1] <- walker[i-1,1]+step_length}
> }
> else {
> if (walker[i-1,2] == 0) {where_to[1,2] <- side_length
> } else {where_to[1,2] <- walker[i-1,2]-step_length}
> }
>
> walker[i,1:2] <- where_to
> }
>
> walker[i,3] <- as.numeric(rownames(over(SpatialPoints(walker[i,1:2]),
> vpl,returnList= TRUE)[[1]]))
>
>
> if(plot){
> require(ggplot2)
> p <- ggplot(walker, aes(x = x, y = y))
> p <- p + geom_path()
> print(p)
> }
>
> return(walker)
> }
> try(transits <- random_walk(5000,1),silent=F)
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