Aslo, this function seems to wipe out my file
zipmaps1a <- unionSpatialPolygons(zipmaps1, IDs=paste(zipmaps1$ZCTA,
zipmaps1$NAME, sep = " "))
when I run names(zipmaps1a), after I run the above command I get NULL
On Wed, Apr 29, 2009 at 12:11 PM, Alina Sheyman <alina...@gmail.com> wrote:
> Using examples in Chapter 5, I am trying to get rid of non-unique polygons.
> I'm working with a Massachusetts shapefile by zips. The file consists the
> following fields
> ZCTA NAME LSAD LSAD_TRANS
>
> I've done the following to get rid of duplicate records
>
> > zipmaps1_df <- as(zipmaps1, "data.frame")
> [!duplicated(zipmaps1$LSAT_TRANS)]
> > row.names(zipmaps1_df) <- zipmaps1_df$LSAD_TRANS
> > zipmaps1a <- SpatialPolygonsDataFrame(zipmaps1, zipmaps1_df) ,
>
> but get the following error message
> Error in SpatialPolygonsDataFrame(zipmaps1, zipmaps1_df) :
> row.names of data and Polygons IDs do not match
>
>
> How do I find out what field R is treating as Polygon ID, so that I can set
> my row.names to that?
>
>
>
> On Wed, Apr 29, 2009 at 2:42 AM, Roger Bivand <roger.biv...@nhh.no> wrote:
>
>> On Tue, 28 Apr 2009, Alina Sheyman wrote:
>>
>> I'm trying to combine two shapefiles using
>>> zipmaps5 <- spRbind(zipmaps1,zipmaps2)
>>>
>>> and getting the following error message
>>> Error in spRbind(as(obj, "SpatialPolygons"), as(x, "SpatialPolygons")) :
>>> non-unique polygon IDs
>>>
>>> Does anyone know how I can get rid of duplicate polygons in a shapefile?
>>>
>>
>> This isn't the problem. The real problem is that zipmaps1 and zipmaps2
>> have non-unique polygon IDs, so that it isn't obvious to the function what
>> you want to do. By default:
>>
>> sapply(slot(zipmaps1, "polygons"), slot, "ID")
>>
>> is set to the FID of the shapefile in readOGR() and equivalently in
>> readShapeSpatial() in maptools. These typically run 0:(n-1). For two
>> objects, they obviously overlap. Please use spChFIDs() methods in maptools
>> to assign IDs that are unique for the output object; in the worst case:
>>
>> zipmaps1 <- spChFIDs(zipmaps1, paste("map1", sapply(slot(zipmaps1,
>> "polygons"), slot, "ID"), sep="_"))
>>
>> and a different "map*" string for zipmaps2 will work, but a unique,
>> meaningful ID is best.
>>
>> This is covered in detail in the code examples for Chapter 5 in our book,
>> and on the help page for ?"spChFIDs-methods".
>>
>> Hope this helps,
>>
>> Roger
>>
>>
>>> thank you!
>>>
>>> [[alternative HTML version deleted]]
>>>
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo@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.biv...@nhh.no
>>
>>
>
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