[R-sig-Geo] Extracting data/value

[Alexander Brenning]

Hi Mikael,

you can use some of the functions in the RSAGA package to extract values 
from a file (grid/shapefile) or data.frame and attach them to a 
data.frame with point locations.

If I may assume that 'indata' is an grid, try any of

   pick.from.ascii.grid
   pick.from.saga.grid
   rsaga.add.grid.values.to.points

(Only the latter actually uses SAGA itself, the former are independent 
of SAGA. The pick.* functions work on data.frames, the rsaga.* on files.)

I 'indata' is a shapefile, try

   pick.from.shapefile

And if 'indata' is another data.frame, try

   pick.from.points

If you choose method="krige" in the pick.* functions, this is just a 
quick-and-dirty ordinary kriging that should work without problems on 
dense point data; it would be fun to plug a more intelligent automatic 
interpolation procedure into these functions...

I hope this helps...
   Alex


Mikael Carlsson wrote:
> Dear readers,
> 
> I have one file look like
> ew;ns;cu;zn
> 1234567;7654321;23.4;13.7
> name indata
> load with read.table command
> 
> another file look like
> 2;cu;zn
> name parmlst
> also load with read.table
> 
> I want to do as follows
> 
> cu.v <- as.vector(cu)
> zn.v<- as.vector(zn)
>  
> but using a for loop, like
> 
> for (i in 1:2)
> {
> some good code for generating file name <- as.vector(some good code)
> #cu and zn in file name extracting value for cu and zn from indata
> }
> 
> 
> I have try almost everyting, using
> paste()
> noquote()
> but it won't work, can only extract cu not the value 23.4 in the as.vector 
> operation
> this 
>> noquote(paste(parmlst[[i+4]],".v",sep="")) <- 
> as.vector(eval(noquote(paste(parmlst[[i+4]]))))
> Error in noquote(paste(parmlst[[i + 4]], ".v", sep = "")) <- 
> as.vector(eval(noquote(paste(parmlst[[i +  : 
>   could not find function "noquote<-"
> - - - - - - - - - - - -
>> test.v <- as.vector(noquote(paste(parmlst[[i+4]])))
>> print(test.v)
> [1] "zn"
> when it should be 13.7
> 
> Running R 2.8.0 on Win NT
> 
> 
> Regards,
> Mikael
> 
> 
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> 
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-- 
Alexander Brenning
brenning at uwaterloo.ca - T +1-519-888-4567 ext 35783
Department of Geography and Environmental Management
University of Waterloo
200 University Ave. W - Waterloo, ON - Canada N2L 3G1
http://www.fes.uwaterloo.ca/geography/faculty/brenning/