[R-sig-Geo] combining polygons from shapefiles...

[Roger Bivand]

On Wed, 2 Dec 2009, Sean O'Riordain wrote:

> Hello again,
>
> I've tried
>    new.refs.for.CA <-
> as.character(seq(from=max(as.numeric(row.names(LA)))+1,length=nrow(CA)))
> # which takes about 0.15 secs...
>    ca1 <- spChFIDs(CA, new.refs.for.CA)
> # has been running now for more than 48 minutes (or at least 48 mins
> CPU on this winbox)  is this right?
> # It was running for about 15minutes and then I tried restarting it in
> a cleaner
> # environment... but it's still taking *ages*
> #
> # it was my intention then of saying
>    S1 <- spRbind(LA, ca1)
>
> but both LA and CA have about 12,000 rows... and it's been running now
> for quite a few minutes and I'm surprised it hasn't finished... is
> this "normal" ?

It is only coded as a for loop in R, and shapefiles used in typical 
applications in R have at most hundreds of entities, although this size 
is encountered without substantial trouble. Timings may vary depending on 
object sizes too, if copying is involved internally.

This goes on the TODO list for coding in C.

Roger

>
> Thanks,
> Sean
>
>
> On Wed, Dec 2, 2009 at 3:18 PM, Sean O'Riordain <seanpor at acm.org> wrote:
>> Thanks Roger,
>>
>>> head(row.names(LA))
>> [1] "0" "1" "2" "3" "4" "5"
>>> head(row.names(CA))
>> [1] "0" "1" "2" "3" "4" "5"
>>>
>>
>> I'll have a look at these and get back with my results.
>>
>> Kind regards,
>> Sean
>>
>>
>> On Wed, Dec 2, 2009 at 3:07 PM, Roger Bivand <Roger.Bivand at nhh.no> wrote:
>>> On Wed, 2 Dec 2009, Sean O'Riordain wrote:
>>>
>>>> Good afternoon,
>>>>
>>>> I've been making good progress in the last few weeks thanks to this
>>>> list, along with Roger and Adrians' books and some great geo-packages.
>>>>
>>>> I'm trying to combine some shapefiles...
>>>>
>>>> library(maptools)
>>>> CA <- readShapePoly('ca.shp')
>>>> LA <- readShapePoly('la.shp')
>>>>
>>>> Now I want to combine these two into a bigger object...
>>>>
>>>> I've searched the books and the internet and I've tried a number of
>>>> things... including...
>>>>
>>>>> class(LA)
>>>>
>>>> [1] "SpatialPolygonsDataFrame"
>>>> attr(,"package")
>>>> [1] "sp"
>>>>>
>>>>> class(CA)
>>>>
>>>> [1] "SpatialPolygonsDataFrame"
>>>> attr(,"package")
>>>> [1] "sp"
>>>>>
>>>>>    S1 <- unionSpatialPolygons(CA, LA)
>>>>
>>>> Loading required package: gpclib
>>>> General Polygon Clipper Library for R (version 1.4-4)
>>>>       Type 'class ? gpc.poly' for help
>>>>
>>>> Error in unionSpatialPolygons(CA, LA) : input lengths differ
>>>>>
>>>>>
>>>>> S1 <- spRbind(CA, LA)
>>>>
>>>> Error in spRbind(as(obj, "SpatialPolygons"), as(x, "SpatialPolygons")) :
>>>>  non-unique polygon IDs
>>>>>
>>>
>>> Correct. Look at row.names(CA) and row.names(LA). Do something of your
>>> choice to disambiguate them and re-assign with spChFIDs() - since you refer
>>> to the ASDAR book, there is an example in chapter 5, sections 5.4 & 5.5, pp.
>>> 120-126. You'll also see that your reading of how to use
>>> unionSpatialPolygons() did not agree with that in the function, which is to
>>> dissolve Polygons objects within an existing SpatialPolygons object.
>>>
>>> Hope this helps,
>>>
>>> Roger
>>>
>>>>
>>>> Any ideas please?
>>>>
>>>> Thanks in advance!
>>>> Sean
>>>>
>>>> _______________________________________________
>>>> R-sig-Geo mailing list
>>>> R-sig-Geo at stat.math.ethz.ch
>>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>>
>>>
>>> --
>>> 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
>>>
>>>
>>
>

-- 
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