On 08/08/2011 05:04 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?
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@i) ### I know this doesn't work, but this is the
question... what grammar could I use?
}
usually one doesn't want to directly access S4 slots, but instead use
accessors defined by the author, e.g., completeObs(myPCA). The idea is
that the implementation of the class might deviate from the interface.
Methods might be documented on the class help page
class(myPCA)
class?pcaRes
or discoverable
showMethods(class="pcaRes", where=getNamespace("pcaMethods"))
Martin
################
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@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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