overlay() in raster package
Oliver,
The function passed to overlay should be work if the arguments are
vectors; but your function only works if the arguments are single
numbers.
Rather than this:
fun = function(x,y) {
if (is.na(x)) {
if (y==1) { return(0)
} else { return(x) }
} else { return(x) }
}
Do this:
fun = function(x,y) {
x[is.na(x) & y==1] <- 0
return(x)
}
Robert
On Thu, Feb 25, 2010 at 7:23 AM, Wearn, Oliver
<oliver.wearn08 at imperial.ac.uk> wrote:
Thanks Kamran, unfortunately I don't think the placement of 'else' has any effect - the same errors arise.
To answer the request for more details, here's a self-contained version of what my data pretty much looks like:
require(raster)
rs <- raster(system.file("external/test.grd", package="raster"))
ENN.500<-reclass(rs,rclmat=matrix(c(200,250,NA),ncol=3,byrow=T))
forest.cover<-reclass(rs,rclmat=matrix(c(0,160,0,160,290,1,290,xmax(rs),0),ncol=3,byrow=T))
plot(stack(forest.cover,ENN.500))
Cheers,
Oliver
________________________________________
From: Kamran Safi Radolfzell [ksafi at mail.orn.mpg.de]
Sent: 25 February 2010 14:42
To: Wearn, Oliver; r-sig-geo at stat.math.ethz.ch
Cc: r-sig-geo-bounces at stat.math.ethz.ch
Subject: Re: [R-sig-Geo] overlay() in raster package
Hi Oliver,
don't really understand what you are trying to do with the overlay, but the
"if" issue might be due to the wrong use of your "else".
if(...)
{
...
}else{ ?#important to have else on the same line
...
}
This might help.
If you need more help on the overlay, I guess more details would be helpful.
hth
Kami
On Thu, 25 Feb 2010 14:34:51 +0000, Wearn, Oliver wrote
Dear all,
I'm trying to use the overlay() function in the raster package, but
can't get 'if' clauses to work. Can anyone help?
I have two rasters, the first of which I would like to modify,
depending on the value in the second (a forest cover raster).
Specifically, if the value in the first (called ENN.500) is NA, I
would like to change the value to zero, but only if the value in the
forest cover raster is 1 (otherwise the value should just be left).
So, I tried:
test <- overlay(x = ENN.500,y = forest.cover,fun = function(x,y) {
? if (is.na(x)) ?{
? ? if (y==1) ?{
? ? ? return(0)
? ? }
? ? else {
? ? ? return(x)
? ? }
? }
? else {
? ? return(x)
? }
})
...but I'm guessing overlay() doesn't work like this? I'm getting
the following errors:
Error: object 'applymethod' not found
In addition: Warning message:
In if (is.na(x)) { :
? the condition has length > 1 and only the first element will be used
I also tried:
test <- overlay(x = ENN.500,y = forest.cover,fun = function(x,y) {
? if (x[is.na(x)]) ?{
? ? if (y[y==1]) ?{
? ? ? return(0)
? ? }
? ? else {
? ? ? return(x)
? ? }
? }
? else {
? ? return(x)
? }
})
...which returned the following error:
Error in .overlayList(rasters, fun = fun, filename = filename,
datatype = datatype, ?: ? cannot use this formula
The alternative would be to use arithmetic operators:
ENN.500[is.na(ENN.500] <- 0
forest.cover[forest.cover==0] <- 1
result <- ENN.500*forest.cover
...but it says in ?overlay that this is slow for very large rasters
(which I will be using), so I'm guessing I should try not to use
this method?
Thanks, in advance, for any help whatsoever.
Oliver
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