>>> Ted Harding <[EMAIL PROTECTED]> 03/10/05 09:13AM >>> >> On 10-Mar-05 Gabor Grothendieck wrote: >> > <Ted.Harding <at> nessie.mcc.ac.uk> writes: >> >: [...] >> >: As Sander says, "Not sure where you would derive the time zone!". >> >:
[snip] >> The only completely general mechanism I can think of would >> consist of >> >> a) a named list of boundary contours I found a shapefile of time zones at: http://openmap.bbn.com/data/shape/timezone/ A google search on the keywords timezone & shapefile finds a few other possibilities. >> b) a function which, for each name in the list, returns >> the TZ name The "maptools" package can read in the above shapefile and convert it to a list of polygons and the "sgeostat" has an "in.polygon" function to see if a point is in a given polygon. The following code worked for me: library(maptools) tz <- read.shape('c:/maps/WrldTZA') plot(tz) plot(tz,xlim=c(-150,-50), ylim=c(20,50)) mappoly <- Map2poly(tz) library(sgeostat) tmp <- sapply(mappoly, function(x){ x <- na.exclude(x) in.polygon( -110, 42, x[,1], x[,2] ) } ) tz$att.data[tmp,] the -110 and 42 come from me plotting the map and using locator to approximate where I am at. I was actually suprized at how quick the sapply was (under a second on my fairly fast pc (windows 2000)). It shouldn't be too hard to convert this into a more general function. Greg Snow, Ph.D. Statistical Data Center [EMAIL PROTECTED] (801) 408-8111 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
