[R-sig-Geo] subsetting terra::raster

[Michael Sumner]

you could do this for a single layer object:

p <- which(values(r) > 0)    #  Possibly faster to use values(r > 0) > 0
cbind(xyFromCell(r,p),extract(r,p))

as long as getting all values is memory-safe (I'm not sure if there's a
Which analog in terra).

HTH



On Tue, Jul 14, 2020 at 4:02 PM Herr, Alexander (L&W, Black Mountain)
<Alexander.Herr using csiro.au> wrote:

> You are right,
>
> What I really want is extract cell coordinates and their values for cells
> with values >0
>
>
>
> So I could use in raster
>
> xyz <- rasterToPoints(r, fun=function(x){x>0}, xy=T)
>
> or
>
> Which(r>0,cells=T)->p
>
> cbind(xyFromCell(r,p),extract(r,p))
>
>
>
> what’s the terra alternative?
>
>
>
>
>
>
>
>
>
> *From:* Michael Sumner <mdsumner using gmail.com>
> *Sent:* Tuesday, 14 July 2020 2:41 PM
> *To:* Herr, Alexander (L&W, Black Mountain) <Alexander.Herr using csiro.au>
> *Cc:* r-sig-geo using r-project.org
> *Subject:* Re: [R-sig-Geo] subsetting terra::raster
>
>
>
> The second argument to xyFromCell is a *cell number*, but in `r[r>0]` you
> have a *cell value*, which may not be what you want.
>
>
>
> It's the r[r > 0] part that's not working in terra, so you could do this
> as a workaround ...
>
>
>
> xy <- xyFromCell(r, values(r)[values(r) >0])
>
>
>
> (but are your cell values really intended for use as cell numbers? It's
> certainly useful for that but probably uncommon).
>
>
>
> Your code also did not set the extent in the terra object, or set.seed so
> there's several steps that lack compatibility.
>
>
>
> Cheers, Mike
>
>
>
>
>
> On Tue, Jul 14, 2020 at 2:18 PM Herr, Alexander (L&W, Black Mountain) <
> Alexander.Herr using csiro.au> wrote:
>
> Hi,
>
> I am moving from raster to terra. I get an error when I adapt the
> following raster code:
> require(raster)
> set.seed(666)
>  reps=10
>  r <- raster( matrix(nrow=reps,ncol=reps, round(rnorm(reps^2),1)))
>  extent(r)<- c(1,101,1,101)
> plot(r)
> xy<-xyFromCell(r,r[r>0])
> z<-r[r>0]
> cbind(xy,z)
>
> Under terra code:
> require(terra)
> r <- rast( matrix(nrow=reps,ncol=reps, round(rnorm(reps^2),1)))
> plot(r)
> xy<-xyFromCell(r,r[r>0])
> Error in r[r > 0] : object of type 'S4' is not subsettable
>
> What am I doing wrong?
>
> Thanks
> herry
>
>
>  in terra
>
>
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>
>
>
>
> --
>
> Michael Sumner
> Software and Database Engineer
> Australian Antarctic Division
> Hobart, Australia
> e-mail: mdsumner using gmail.com
>


-- 
Michael Sumner
Software and Database Engineer
Australian Antarctic Division
Hobart, Australia
e-mail: mdsumner using gmail.com

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