Gets the second nearest neighbor using spatstat's crossdist

nn2.crossdist.r

#get pairwise distances from rp and ponderosa datasets
xpairs <- crossdist(rp, ponderosa)

#Initialize vector container for X.2
X.2 = numeric()

#Sort rows and get second nearest neighbor
for (i in 1:nrow(xpairs) {
  x <- sort(xpairs[i,])[2]   
  X.2 <- append(X.2, x)
}