[R] Permutation test of marked point pattern

From: Jean-Francois Savard <jsavard_at_umd.edu>
Date: Thu 04 May 2006 - 05:01:52 EST


Dear R users,

I am trying to perform a hypothesis test on a marked point pattern. I would like to calculate the mean of the absolute value of the difference of marks between nearest neigbours, randomize the marks among points, then calculate this mean again. Ideally, I would test whether random mean values smaller than the observed mean value occur less than 5% of the time. I suppose 1000 permutations would be a reasonable starting point (the ppp object has 27 points).

so far, I've figured out how to:

-create a marked ppp object: ms.ppp

-calculate my test statistic:

teststat <- mean(abs(markstat(ms.ppp, diff, N=2)))

-randomly allocate marks to a point pattern:
Y <- rlabel (ms.ppp, labels=ms.ppp$marks, permute=TRUE)

I have looked at perm.test{exactRankTests} and perused the R help archive but haven't been able to find how to work the permutation test with a marked ppp object.

I thank you in advance for any help,

J-F Savard
Doctoral Candidate
University of Maryland



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