On 11/09/2010 09:05 PM, Lee Hachadoorian wrote: > > > 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)
It would be rather trivial to make the following work: spdfNew = SpatialPolygonsDataFrame(sp, df, match.ID = "key_field") which would do the same as the last two of your commands. > 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 > -- 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 e.pebe...@wwu.de _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
