[R] S4 classes, some help with the basics

[Duncan Murdoch]

On 08/08/2011 8:04 PM, Mike Williamson wrote:
> Hi All,
>
>      I have tried to find an answer within documentation, but I cannot:
>
> o How can call a class "slot" without knowing the name a priori?

See ?slot.

>
>      E.g., let's say I use the "pcaMethods" library to create a "pcaRes"
> object.  How can I call parts of that object without using the specific
> names of the object in the call?
>
> example code:
>
> library(pcaMethods)
> myMatrix<- matrix(runif(1e4), ncol=100)  ## silly, but sufficient for
> example
> myPCA<- pca(myMatrix)  ## creates a "pcaRes" S4 class
>
> for (i in slotNames(myPCA) ) {
>       summary(myPCA at i)  ### I know this doesn't work, but this is the
> question... what grammar could I use?

summary(slot(myPCA, i))

Duncan Murdoch

> }
>
> ################
>
> I would like to be able to print out the summary for each of the components
> of the class "pcaRes" without knowing a priori the names of those
> components.  I could, for example in the above case, type in
> summary(myPCA at completeObs) to get a summary of the input matrix.  But I HAVE
> TO TYPE "@completeObs".  In the non-S4 world, I could type myPCA[[i]] for
> lists, where "i" could be looping through either the list names, or the list
> indices.  Similarly, I could type myPCA[i] for arrays, where "i" again can
> be either a numeric index or the name.
>
> Without this ability to identify portions within an array / loop context, it
> becomes exceedingly difficult to work in "S4 land".  How is this sort of
> thing done?
>
>                                  Thank you!
>                                           Mike
>
>
>
> ---
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