On Thu, 22 Apr 2010, Paulo van Breugel wrote:
Dear list,
In my GRASS GIS database I have the vector map 'inmap', which is a
vegetation map with different vegetation types defined in column 'VT'. I
want to split the vector map according to the VT in different vector
maps as part of a larger script. I wrote a small script following the
steps described below:
There seems to be something odd about your use of Name= and VT=, perhaps?
Cross-platform quoting is always problematic. Had you considered using R
to subset the vector object if it isn't too large (example in spearfish):
library(spgrass6)
soils <- readVECT6("soils")
labs <- levels(soils$label)
clabs <- as.character(soils$label)
for (i in labs) {
cat(i, "\n")
writeVECT6(soils[clabs == i,], paste("soils", i, sep="_"))
}
or something similar. I have also added extra quote protection in doGRASS
- please check out the current CVS development source from sourceforge,
r-spatial, module spgrass6, with:
param <- list(input=inmap, output=namelist2[i],
where=paste("\"Name", "='", namelist1[i], "'\"", sep=""))
so that automatic quote protection of spaced strings is avoided by
providing the quotes manually, thus for all strings. This may not work
cross-platform - please test and report back.
Hope this helps,
Roger
First I extract the values of the column VT into a character vector
namelist1
> namelist1:
[1] "Acacia and allied vegetation"
[2] "Alpine"
[3] "Bamboo woodland and thicket"
[4] "Bare land"
Because I want to avoid spaces in the names of the resulting vector
maps, I convert namelist1 into namelist2:
> namelist2
[1] "Acacia_and_allied_vegetation"
[2] "Alpine"
[3] "Bamboo_woodland_and_thicket"
[4] "Bare_land"
I am using these two as input for v.extract, using a loop (for this
occassion using doGRASS instead of execGRASS):
for(i in 1:length(namelist1){
param <- list(input=inmap, output=namelist2[i],
where=paste("Name","='",namelist1[i], "'",sep=""))
flags <- c("d")
doGRASS("v.extract", parameters=param, flags=flags)
}
For i=1, the following is send to GRASS:
v.extract -d input=trapnel1 output=Acacia_and_allied_vegetation
where=\"Name='Acacia and allied vegetation'\""
For i=2, the following is send to GRASS:
v.extract -d input=trapnel1 output=Alpine where=Name='Alpine'
In the second example the argument for the second parameter 'where' is
not surrounded by double quotation marks, resulting in an error in the
execution of the command in GRASS. This always seems to happen when the
argument consist of one string without spaces.
For now I am running the same command via system call -
system(paste("v.extract -d input='",inmap, "' output='", namelist3[i],
"' where=\" VT='", namelist1[i], "'\"", sep="")) -, which works fine.
However, I would like to know what/if I am doing something wrong here.
Best regards
Paulo
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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
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