R: substract two columns in a shapefile (but SAGA+R has an bug error)
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$Dem.sgrd
writeOGR(canopy_height, ".", "canopy_height", driver="ESRI Shapefile")
because maptool go out of memory, with rgdal the third column appears empty
(value: 0.0000)
I attached a small file of my data set.
Thanks again for your help and time
Ale
-----Messaggio originale-----
Da: Roger Bivand [mailto:Roger.Bivand at nhh.no]
Inviato: marted? 24 febbraio 2009 10.51
A: Alessandro
Cc: r-sig-geo at stat.math.ethz.ch
Oggetto: Re: [R-sig-Geo] substract two columns in a shapefile (but SAGA+R
has an bug error)
On Tue, 24 Feb 2009, Alessandro wrote:
Dear Researcher, I have a shapefile with two columns "a" and "b" and I wish to subtract a-b to obtain a new column of difference. I tried in SAGA + R with the module "Table calculator for shapes". This worked without an error, but it didn't save the results either. I suspect that this is a bug in the SAGA module. Is there an another code or packages (without GRASS+R) to do operation
with
shapefile?
Why not do it the simple way?
Either:
library(maptools)
my_SPDF <- readShapeSpatial("myfile.shp")
my_SPDF$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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