Help with as.numeric(rownames(over(SpatialPoints(set1, set2, returnList= TRUE)[[1]]))

Sun, Nov 1, 2015 10:35 AM

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)) :

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)

Help with as.numeric(rownames(over(SpatialPoints(set1, set2, returnList= TRUE)[[1]]))

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