Dear Prof. Bivand Tank for help
I tried this cose
library(rgdal)
canopy_height <- readOGR(".", "theme1")
canopy_height$ZDem.sgrd <- canopy_height$Z - canopy_height$Dem.sgrd
writeOGR(canopy_height, ".", "canopy_height", driver="ESRI Shapefile")
because maptool go out of memory, with rgdal the third column appears empty
(value: 0.0000)
I attached a small file of my data set.
Thanks again for your help and time
Ale
-----Messaggio originale-----
Da: Roger Bivand [mailto:roger.biv...@nhh.no]
Inviato: martedì 24 febbraio 2009 10.51
A: Alessandro
Cc: r-sig-geo@stat.math.ethz.ch
Oggetto: Re: [R-sig-Geo] substract two columns in a shapefile (but SAGA+R
has an bug error)
On Tue, 24 Feb 2009, Alessandro wrote:
> Dear Researcher,
>
>
>
> I have a shapefile with two columns "a" and "b" and I wish to subtract a-b
> to obtain a new column of difference. I tried in SAGA + R with the module
> "Table calculator for shapes". This worked without an error, but it didn't
> save the results either. I suspect that this is a bug in the SAGA module.
>
>
>
> Is there an another code or packages (without GRASS+R) to do operation
with
> shapefile?
Why not do it the simple way?
Either:
library(maptools)
my_SPDF <- readShapeSpatial("myfile.shp")
my_SPDF$ab <- my_SPDF$a - my_SPDF$b
writeSpatialShape(my_SPDF, "mynewfile")
or:
library(rgdal)
my_SPDF <- readOGR(".", "myfile")
my_SPDF$ab <- my_SPDF$a - my_SPDF$b
writeOGR(my_SPDF, ".", "mynewfile", driver="ESRI Shapefile")
Insert a summary(my_SPDF) to check that a and b are what you think, and
that ab has been created. It won't work if a and/or b are strings.
Roger
>
>
>
> Thanks
>
>
>
> Ale
>
>
> [[alternative HTML version deleted]]
>
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> R-sig-Geo@stat.math.ethz.ch
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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.biv...@nhh.no
theme1.shp
Description: Binary data
theme1.shx
Description: Binary data
theme1.dbf
Description: Binary data
theme1.sbn
Description: Binary data
theme1.sbx
Description: Binary data
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