[R] a for loop to lapply

[Dieter Menne]

alaios wrote:
> 
> I am trying to learn lapply.
> I would like, as a test case, to try the lapply alternative for the 
> Shadowlist<-array(data=NA,dim=c(dimx,dimy,dimmaps))
> for (i in c(1:dimx)){
>     Shadowlist[,,i]<-i
> }
> ---so I wrote the following---
> returni <-function(i,ShadowMatrix) {ShadowMatrix<-i}
> lapply(seq(1:dimx),Shadowlist[,,seq(1:dimx)],returni)
> 
> 
The basic problem is that you have an array, but you name it "list". This is
valid code, but by calling it so you shot a list-bullet into your
vector-foot. An array should be treated like an array, and the best way to
fill it uses simple vectoring. No loop, no xapply needed.

Use lapply if you have a data.frame or (more generic) a real list, which can
contain rather heterogeneous components. And try to forget what you learned
in your c++ course: Seeing 
 
lapply(,Shadowlist[,,seq(1:dimx)],)

to fill Shadowlist tell me that it must be wrong, because R (in all
recommended cases) never "fills" a parameter passed to it like c(++) can do.
You should always have something like:

Shadowlist <- lapply(....)

Dieter
#------ 
dimx=2 # don't forget to make the example self-contained
dimy=3
dimmaps=3
ShadowArray<-array(data=NA,dim=c(dimx,dimy,dimmaps))

# Are you shure you mean "dimx" ? But let's assume it is correct
for (i in c(1:dimx)){
    ShadowArray[,,i]<-i
}
ShadowArray

ShadowArray<-array(data=NA,dim=c(dimx,dimy,dimmaps))
ShadowArray[,,1:dimx]<-1:dimx
ShadowArray




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