Read in data and find nearest neighbor in R

read_nn.R

require("ggplot2") # for plots
require("plyr") # for processing dataframes
# the function to find nearest neighbors
# requires data with x, y, and val columns (val is a unique identifier)
find.nn<-function(in.df) {
  ddply(in.df,.(val),function(c.group) {
    cur.val<-c.group$val[1]
    cur.x<-c.group$x[1]
    cur.y<-c.group$y[1]
    all.butme<-subset(in.df,val!=cur.val)
    all.butme$dist<-with(all.butme,sqrt((x-cur.x)^2+(y-cur.y)^2))
    min.ele<-subset(all.butme,dist<=min(all.butme$dist))
    min.ele.order<-order(runif(nrow(min.ele)))
    min.ele<-min.ele[min.ele.order,]
    out.df<-data.frame(x=cur.x,y=cur.y,
               xe=min.ele$x[1],ye=min.ele$y[1],vale=min.ele$val[1],dist=min.ele$dist[1])
    out.df
    })
}

in.table<-read.csv("sample-a.csv")
# add a val column
in.table<-cbind(in.table,val=1:nrow(in.table))
# calculate the nearest neighbor distance
in.table.nn<-find.nn(in.table)
# plot each point and color it by how far away the nearest neighbor is
ggplot(in.table.nn,aes(x=x,y=y,color=dist))+geom_point()+coord_equal()+labs(title="Points and NN Distance",color="NN Distance")