On 02/10/2012 08:00 AM, Tom Gottfried wrote: > Edzer, > > Am 09.02.2012 17:58, schrieb Edzer Pebesma: >> >> >> On 02/09/2012 05:02 PM, Etienne B. Racine wrote: >>> It seems that sampleRandom isn't so random. >>> >>> # try this : >>> library(raster) >>> r<- raster(matrix(1:25, 5, 5)) >>> sampleRandom(r, 25) >>> ## 1 6 11 16 21 2 7 12 17 22 3 8 13 18 23 4 9 14 19 24 5 10 15 >>> sampleRandom(r, 25) >>> ## 1 6 11 16 21 2 7 12 17 22 3 8 13 18 23 4 9 14 19 24 5 10 15 >>> >>> I haven't seen any documentation about this behavior. >>> >> >> Isn't the more important question whether you saw documentation that is >> in conflict with this behaviour? > > taking that to the extremes: undocumented software always works perfectly.
And is useless, too -- no, these kind of questions are often highly useful because they improve software or the documentation, and both are valuable activities. >From the base::sample analogy, I would have expected a random permutation, so IMO it would make sense to document this is not the case (the function is not called sample, anyway -- question are: what would the random permutation be good for? and would it still perform well when the image is huge?) > > (By the way I've heard that's the way ESRI did it with their > "Geostatistical Analyst") > You might be mixing up things here or have outdated information; the author of Geostatistical Analyst published in 2011 (at ESRI press) a nearly 1000 page e-book "Spatial Statistical Data Analysis for GIS users", which obviously addresses ArcGIS, but also R and WinBugs for areas where ArcGIS does not offer solutions. He is on this list, too. -- Edzer Pebesma Institute for Geoinformatics (ifgi), University of Münster Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251 8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de http://www.52north.org/geostatistics [email protected] _______________________________________________ R-sig-Geo mailing list [email protected] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
