[R-sig-Geo] question on adding variable to .dbf file

[Stephen Sefick]

Look at the foreign package

?read.dbf

On Mon 08 Oct 2012 09:07:33 AM CDT, Zijdeman, R.L. (Richard) wrote:
> Dear all,
>
> I am trying to add and then display regional characteristics (e.g. population size) to an existing map. The map comes as a .shp file, including .sbn, .sbx, .shx and .dbf file and portrays municipality borders.  However, once I have added a new column to the .dbf file, I am unable to reread the .shp file and get the following error:
> Error in `row.names<-.data.frame`(`*tmp*`, value = value) :   invalid 'row.names' length.
>
> Here's what I do:
>
> # To read the map:
> munis<-readShapePoly("nl_1890.shp")
>
> # To merge the new column with the original data:
> munis2<-merge(munis,y, by.x="acode", by.y="hplts_adam_code", all.x)
> # acode is key in the original file, to be merged with "hplts_adam_code" from the file containing regional information
>
> head(munis2,3)
> # acode GM_1890      GM_NAAM cbscode   famprop
> # 1 10002    0136    Zuidlaren     136 1.0000000
> # 2 10005    0086   Opsterland      86 1.0000000
> # 3 10007    0981        Vaals     981 0.1250000
>
> # Since I thought it was important, I changed the order of the variables back to the original order, with the added column "famprop" as last one:
> munis2<- munis2[c(2,3,4,1,5)]
> # GM_1890    GM_NAAM cbscode acode famprop
> # 1    0136  Zuidlaren     136 10002   1.000
> # 2    0086 Opsterland      86 10005   1.000
> # 3    0981      Vaals     981 10007   0.125
>
> # next I write munis2 into the .dbf file (using the original name for the .dbf file)
> write.dbf(munis2,"nl_1890")
>
> # finally I try to read in the .shp file again
> munis2shp<-readShapePoly("nl_1890.shp")
>
> # but this result in the following error:
> Error in `row.names<-.data.frame`(`*tmp*`, value = value) :
>   invalid 'row.names' length
>
> I am quite novice to R and mapping data, so any advice on either code or my approach is very much appreciated.
>
> Best,
>
> Richard
>
>
>
>
>
>
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>
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-- 
Stephen Sefick
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Auburn University                                         
Biological Sciences                                      
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