R help - Oct 2012 - mapply instead for loop

Hi all!
 
My question in about using mapply instead for loop. Below is a example with for
loop: Is it posible to give same results with mapply function?
 
Thanks for help!
 
OV
 
x <- 1:10
y <- 1:10
xyz <- data.frame(expand.grid(x,y)[1], expand.grid(x,y)[2], z = rnorm(100))
names(xyz) <- c("x", "y", "z")
head(xyz)
size <- 2
output <- NULL
 
### for loop
 
for(i in 1:dim(xyz)[1]){
x0 <- xyz[i, "x"]
y0 <- xyz[i, "y"]
xyzSel <- xyz[xyz$x >= (x0 - size) & xyz$x < (x0 + size) &
xyz$y >= (y0 - size) & xyz$y < (y0 + size), ]
output[i] <- min(xyzSel$z)
}
output
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On 30.10.2012 20:01, Omphalodes Verna wrote:
> Hi all!
>
> My question in about using mapply instead for loop. Below is a example with
for loop: Is it posible to give same results with mapply function?
>
> Thanks for help!
>
> OV
>
> x <- 1:10
> y <- 1:10
> xyz <- data.frame(expand.grid(x,y)[1], expand.grid(x,y)[2], z =
rnorm(100))
> names(xyz) <- c("x", "y", "z")
> head(xyz)
> size <- 2
> output <- NULL
>
> ### for loop
>
> for(i in 1:dim(xyz)[1]){
> x0 <- xyz[i, "x"]
> y0 <- xyz[i, "y"]
> xyzSel <- xyz[xyz$x >= (x0 - size) & xyz$x < (x0 + size) &
xyz$y >= (y0 - size) & xyz$y < (y0 + size), ]
> output[i] <- min(xyzSel$z)
> }
> output
Yes:

output <- mapply(function(x0, y0)
     min(xyz[(xyz$x >= (x0 - size) & xyz$x < (x0 + size)) & (xyz$y
>=
(y0 - size) & xyz$y < (y0 + size)), "z"]),
     xyz$x, xyz$y)

Uwe Ligges


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