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R: Moran's I
2 messages · Theresa Sinicrope Talley, Roger Bivand
On Fri, 4 Mar 2005, Theresa Sinicrope Talley wrote:
Hi- I would like to assign distance classes (lags) to the moran's I test in R. I don?t have equally spaced points since I was mapping shrubs across a landscape (vs. an experiment or survey in a grid). I somehow need to select points based on the distances in the distance matrix (i.e., I need to select all pairs of points that occur 0-25 m from each other, 25-50 m, etc...). Does anyone have code or a detailed procedure for subsampling or dividing a dataset into distance classes for moran?s I (or mantel test)? I know there is sp.correlogram but I need significance values for each I value and I need to use distance lags, not lags of number of polygons.
If you need to follow this up further, please consider moving your reply to the r-sig-geo list (access from http://www.r-project.org/Rgeo). In the spdep package, you can define distance based lists of neighbours by: nb0_25 <- dnearneigh(points, d1=0, d2=25) nb25_50 <- dnearneigh(points, d1=25, d2=50) then calculate Moran's I (moran.test()) or a chosen Mantel test (sp.mantel.mc()) using these lists. You are right that sp.correlogram() is not appropriate in this setting.
Any suggestions would be appreciated. Best wishes, theresa
Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Breiviksveien 40, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93 e-mail: Roger.Bivand at nhh.no