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@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) [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list R-sig-Geo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo