On 11/09/2010 02:12 PM, Roger Bivand wrote: > On Tue, 9 Nov 2010, Lee Hachadoorian wrote: > >> The example from the documentation for nbdists() uses two predefined >> objects (columbus and col.gal.nb), so it's not clear to me how >> coordinates are being matched (see below) > Good question. None of these functions check by matching, they assume > that the order is correct, and it is the user's responsibility to make > sure that it is. I'll try to revise the help pages to make this clearer. > > Do you think that the functions should check? If so, how, given that > by default matrices do not have row names?
This probably isn't too well thought out, but perhaps (1) coordinates() could have a row.names parameter which, like poly2nb() would default to NULL. Then I would generate a matrix with row names using > coords = coordinates(columbus, row.names = columbus$COLUMBUS_I) (2) nbdists() and related functions would match based on row name, either automatically IF both the nb object and the coordinates matrix had row names, or with a parameter like match.ID = TRUE. The background here is that I am a recent R convert coming from the SQL world, so I am used to matching things based on key columns rather that the "reorder the vectors and stick them next each other" approach that is common in the R world. So, for example to join attribute data to a SpatialPolygonsDataFrame, instead of the approach you use in your book of using match to generate an ordering vector then spCbind the attribute data frame, I will row.names(spdf) = as.character(spdf$key_field) sp = as(spdf, "SpatialPolygons") row.names(df) = df$key_field spdfNew = SpatialPolygonsDataFrame(sp, df, match.ID = TRUE) Partially my own limitations, but it does seem to use fewer lines of code when joining several different data frames of attribute data when I'm doing exploratory visualization. --Lee -- Lee Hachadoorian PhD Student, Geography Program in Earth & Environmental Sciences CUNY Graduate Center _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
