I want to thank everyone for their comments and suggestions. P. Burns' S Poetry I think will be a lot of help and I thought it was really poetry:). So will the other references that were provided by I believe Mr Kane. The other replies provided me some great insights.
If I understand R uses the $ and [[]] like java uses the . (dot) notation for accessing components of classes and objects. If the java class or object being accessed by the . notation is specifically a list, container, vector, or array type you use the element operator which is the parenthesis in java but R uses []. This helps be visualize what I am trying to do if I am correct with my interpretation. Thank all of you so much. Joe Thomas Lumley wrote: > On Tue, 24 Oct 2006, Joe W. Byers wrote: >> following code produces a 5 element list of 2X5 random numbers that I >> then convert to a 2X5X5 matrix. >> cov<-matrix(c(.4,-.1,-.1,.3),nrow=2,ncol=2) >> rnds<-NULL; >> for (i in 1:5){ >> t1<-rnorm(5,cov) >> t2<-rnorm(5,cov) >> t3<-rbind(t1,t2) >> rnds[i]<-list(t3) >> } >> >> rnds.matrix<-array(unlist(rnds),dim=c(2,5,5)); >> >> To access the matrix rnds.matrix I use rnds.matrix[x,y,z]. This I >> understand. >> >> To access the list I user [[z]][x,y]. This I do not understand. I >> found by chance this reference notation in an old mailing list that >> helped me. >> > > Yes, this can be confusing. One reason that it is confusing is that the > rules appear to be different (though they aren't) for vectors and lists. > > The single bracket [ extracts a subvector, and the double bracket [[ > extracts an element. That is, with > a<-list(b=1,c=2,d=3) > you can extracts the first element of a, >> a[[1]] > [1] 1 > or a sublist with the first two elements >> a[1:2] > $b > [1] 1 > > $c > [1] 2 > or a sublist with just the first element >> a[1] > $b > [1] 1 > > The same is true for numeric or character vectors, but there an element > and a subvector of length one are the same, so the distinction between [[ > and [ is harder to understand. >> b<-1:10 >> b[1:2] > [1] 1 2 >> b[1] > [1] 1 >> b[[1]] > [1] 1 > > -thomas > > ______________________________________________ > R-help@stat.math.ethz.ch 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. > ______________________________________________ R-help@stat.math.ethz.ch 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.