[R] 4D data acsess

[Peter Ehlers]

On 2011-06-29 15:02, David Winsemius wrote:
>
> On Jun 29, 2011, at 4:56 PM, katarv wrote:
>
>> Hi Sarah,
>>
>> I use readMat function, from R.matlab function.
>>
>> str(X) tells that
>>
>> X : num [1:64, 1:64, 1:21, 1:300]  as I said, the first 3 columns
>> are x,y,z
>> coordinates. And I need all values in the last column correcponding
>> to a
>> given (x,y,z) coordinate.
>
> You should be able to access those values with:
>
> X[1,1,1, ]
>
> or equivalently:
>
> X[1,1,1,1:300]
>
>>
>> if you list the values of X,
>
>> then they are non zero, but for some reason R
>> tells that dim(X): NULL
>
> Now that seems a bit odd. What happens if you try:

I think that Katia is not telling us the whole story. According to
its documentation, readMAT returns a *list* named X, presumably in
this case containing just the X element. So my guess is that str(X)
actually said:

  List of 1
  $ X : num [1:64, 1:64, 1:21, 1:300] ....

Naturally, dim(X) is NULL.

Katia probably just needs to do do two things:
1. extract array X from list X (e.g. with X <- X$X).
2. learn to read the documentation of functions she's trying to use.

Peter Ehlers

>
> Y<- X
> dim(Y)<- c(64,64,21,300)
> Y[ 1, 1, 1, ]
>
>>
>> --
>> View this message in context: http://r.789695.n4.nabble.com/4D-data-acsess-tp3633552p3634004.html
>> Sent from the R help mailing list archive at Nabble.com.
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> West Hartford, CT
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.