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

[Herr, Alexander (L&W, Black Mountain)]

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<mailto: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<mailto:mdsumner using gmail.com>

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