Dear Kingsford
Thank you very much for your suggestion. It turns out I had downloaded an old
version of raster. I also got a reply from the R-forge website with other
suggestions.
In case anybody using the R-help list is interested, here is the link:
http://r-forge.r-project.org/forum/message.php?msg_id=1269
Regards,
Michelle
----- Original Message ----
From: Kingsford Jones <kingsfordjo...@gmail.com>
To: Michelle Greve <michelle_gr...@yahoo.com>
Cc: R-help@r-project.org
Sent: Sunday, February 22, 2009 7:32:58 PM
Subject: Re: [R] Extracting xy from raster based on raster value
Hi Michelle,
The r-sig-geo list would be the ideal place for this question since
the authors of 'raster' would be likely to see it.
I haven't used the raster package before, but this seems to work:
#install.packages("raster", repos="http://R-Forge.R-project.org";)
r <- raster()
r <- setValues(r, sample(1:27, ncell(r), replace=1))
plot(r)
r[] <- r[]==1
plot(r)
If you'd rather have the non-1 cells be NA, just replace 'r[]==1' with
'ifelse(r[]==1, 1, NA)'
hth,
Kingsford Jones
On Sat, Feb 21, 2009 at 8:46 AM, Michelle Greve
<michelle_gr...@yahoo.com> wrote:
> I have a raster (which I called glc), which I read
> into R as a raster with "raster.create.from.file" from the raster package
> (R-forge). Values in glc range between 1 and 27 (whole numbers only). I'd
> like to extract all cells with a value of 1 to create
> a new raster with only the cells that have a value of 1, or to extract
> the xy values of all raster cells with a value of 1. Could you please
> help me along? I have tried using several of the functions in the
> raster help package, e.g. "raster.get.xy.from.cell", but do not know
> how to specify glc=1. I have tried to use e.g.:
> glc1<-raster.get.xy.from.cell(glc,glc==1)
> glc1<-raster.get.xy.from.cell(glc, glc[which(glc==1)])
>
> The reason I specifically used the raster package to read in my files is
> because I have been unable to read my ascii files (which are very big) into R
> using read.asciigrid because the ascii files are so big (and none of the
> various suggestions I found in various R-help archives that I found for
> increasing memory size were sufficient to allow me to read in my ascii
> files). Therefore if alternatively somebody knows of another way to read
> raster or ascii files into R, which would make it easier to conduct the
> extraction I mentioned in my first paragraph, I would appreciate any
> suggestions.
>
> Regards,
> Michelle
>
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