[R] Count of included observations in sp.correlogram

[Robert U]

Dear Rusers,
I’m tryingto figure out what I think is a pretty simple thing for anyone who knows about correlograms.I’ve a regular grid (say 5*5 points) with some quantity associated to eachpoint (count data). I’m trying to verify whether this quantity is regularly /randomly or “clusterdly” distributed on the grid. I’ve decided to give a shotto the sp.correlogram {spdep}. 

I first createda grid using cell2nb:  

grid <- cell2nb(5,5)xyc <- attr(grid,"region.id")xy <-matrix(as.integer(unlist(strsplit(xyc, ":"))), ncol=2, byrow=TRUE)plot(grid,xy) >gridNeighbour list object:Number of regions: 25 Number of nonzero links: 80 Percentage nonzero weights: 12.8 Average number of links: 3.2 I then usedsp.correlogram, and specified “order = 4” since I figured the maximum lagbetween 2 points on a 5 by 5 grid is 4… In sp.correlogram we do not have tospecify a “style” as in moran.test, not sure why so far… anyway. 

results<- sp.correlogram(grid, data$quantity, order=4, method = "I")  print(results,"bonferroni") In the “print” tbale, the count ofobservation per lag order (in brakets) is 25 for each lag. This is what I donot understand, should not this count be changing with lags?  I mean, when you look at the graph of “grid” Iwould have expected a lower number for lag 4 (say only 15 pairs of observationare “that far”) and a way higher number for lag 1… Does that make sens toanyone? regards
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