Re: masking z values (extract or subset on a 3-d array)

Andy,

Maybe this is confusing because the data really ought to be in a dataframe
with factors coding for treatments?

Here's one solution:

foo[,'z',] <- sapply(foo[,'z',], function(x) max(c(x, 0)))

THK

On 5/26/06, Andy Bunn <abunn@xxxxxxxx> wrote:
>
> > > This is driving me nuts. I have a 3-D array that holds x,y,z
> > > coordinates from multiple experiments. I need to clean the
> > data before
> > > making it sp objects. I want to set all z-values < 0 to 0. In a 2-D
> > > matrix this is trivial e.g., x[,x[1,]<0] <- 0. But I'm
> > stumped on how
> > > to do this on a 3-D array without a loop. Given an array:
> > >
> > >   foo <- array(rnorm(24), dim=c(4,3,2))
> > >   dimnames(foo) <-
> > list(NULL,c('x','y','z'),c('Experiment1','Experiment2'))
> > >   foo[,'z',]
> > >
> > > How can I set foo[,'z',]<0 to 0?
> >
> > a <- array(rnorm(64), c(4,4,4))
> > inds <- which(a < 0, arr.ind=TRUE)
> > a[inds] <- 0
> >
>
> Thanks, but I'm looking to set only the values from one dimension to zero.
> As above, I just want to set the 'z' values to 0 if they are less than
> one.
> This works:
>
>   foo <- array(rnorm(24), dim=c(4,3,2))
>   dimnames(foo) <-list(NULL,c('x','y','z'),c('Experiment1','Experiment2'))
>   foo[,'z',]
>   #How can I set foo[,'z',]<0 to 0
>   for(i in 1:2){
>     foo[foo[,'z',i]<0,'z',i] = 0
>   }
>   foo
>
> But it seems like one should be able to do this with apply or just '['.
> I'm
> at a loss.
>
> -A
>
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-- 
Timothy H. Keitt
http://www.keittlab.org/

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