[R-sig-Geo] spplot with quantitative variable

[Matthieu Stigler]

>Hope this helps
yes it does, definitely.. thanks a lot!

Actually you were right, it is just a factor problem, the names were
in factor and the new series I added also :-( I?ll be able to solve
that now, thanks!

2009/8/13, Roger Bivand <Roger.Bivand at nhh.no>:
> On Thu, 13 Aug 2009, Matthieu Stigler wrote:
>
>> Hi
>>
>> I'm new to sptial analysis and just dicovers so I have a really basic
>> question. I could unfortunately not find the answer on  in the tuto,
>> help files or springer book (tough it is sure there :-(). So sorry if
>> the answer is trivila but this would help me a lot!
>>
>> I have a an object say TRY of class "SpatialPolygonsDataFrame"
>> representing a country and its subareas (26). First question, is there
>> a generic function to access the name of the subdivisions?
>> I used the workaround: as.data.frame(TRY)[,"NAME_1"] is there
>> something more elegant? How to extract the values in general?
>> TRY[,"NAME_1"] prints a lot of information beside the series I want.
>
> If the observation (feature) IDs are set to the name, row.names(TRY) would
> work (for recent releases of sp). If they are not so set, you can set them
> by:
>
> TRY1 <- spChFIDs(TRY, as.character(TRY$NAME_1))
>
> (see ?spChFIDs in maptools and examples in ch. 5). I suspect that NAME_1
> is a factor - what does str(as(TRY, "data.frame")) say?
>
>>
>> My problem actually concerns to add a new series (say population) to
>> this dataset, and to plot it...
>>
>> To add the series, I did:
>> data$new<-rnorm(100)
>
> Yes, if the object is TRY, then TRY$new <- will do it. See also ?spCbind
> in maptools if you need more control of the ordering.
>
>>
>> is that the right manner?
>>
>> Then I tried to plot it using spplot() but I hvae the following
>> problem: the colors are just sorted following the order in which the
>> values appear in the series (so the first subdivion with name A...
>> with low pop can have same color as subdivion B with high color). So
>> the data is not sorted correspondly and the colors are totally messed
>> up. I just want to have the colors "increasing " with the population.
>> Furterhmore, my scale just shows the individual values for each
>> subdivision...
>
> This sounds very much as though the variable you are using is a factor,
> which will generate one colour per factor level. Are you reading in data
> that say use a comma as the decimal separator in a locale that expects a
> point (or the reverse)? You can convert a wrongly identified factor to
> numeric by coercing first to character, then sub()stituting the "," with
> "." (or the reverse if necessary, be careful to escape the point as it has
> special meanings in regular expressions), then coerce to numeric. This is
> R FAQ 7.10:
>
> http://cran.r-project.org/doc/FAQ/R-FAQ.html#How-do-I-convert-factors-to-numeric_003f
>
> for the conversion, see ?sub for changing the decimal separator.
>
> Hope this helps,
>
> Roger
>
>>
>> What shoulk I use? Define myself colors palette as in the springer
>> book at section 3,4? Do I do something wrong when adding the variable?
>> I don't understand why I dont get the same result as the example in
>> the demo(gallery):
>>
>> library(sp); library(lattice) # required for trellis.par.set():
>> trellis.par.set(sp.theme()) # sets color ramp to bpy.colors()
>> library(maptools)
>> nc <- readShapePoly(system.file("shapes/sids.shp",
>> package="maptools")[1], proj4string=CRS("+proj=longlat +datum=NAD27"))
>> spplot(nc, "SID79", names.attr = "1979")
>>
>> here the scale does not give the individual values as in my case. Are
>> those object "SID79" and the series I entered so different? I can I
>> caompre them?
>>
>> Thanks a lot!!
>>
>> Matthieu Stigler
>>
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>>
>
> --
> Roger Bivand
> Economic Geography Section, Department of Economics, Norwegian School of
> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
> e-mail: Roger.Bivand at nhh.no
>
>