On Mar 12, 2013, at 3:59 AM, Radford Neal wrote: > Several bugs are present in R-2.15.3 and R-alpha due to > naive copying of list elements. > > The bug below is due to naive copying in subset.c (with > similar bugs for matrices and arrays): > > a<-list(c(1,2),c(3,4),c(5,6)) > b<-a[2:3] > a[[2]][2]<-9 > print(b[[1]][2])
This is an example of lazy evaluation, right? > > Naive copying in mapply.c leads to the following bug: > > X<-1+1 > f<-function(a,b) X > A<-mapply(f,c(1,2,3),c(4,5,6),SIMPLIFY=FALSE) > print(A) > X[1]<-99 > print(A) > Is this a bug in mapply()? or in print()? I thought 'print' should evaluate its argument and "force" the promise to be executed. Or does it just return the same promise as was passed to it? Compare: X<-1+1 f<-function(a,b) X A<-mapply(f,c(1,2,3),c(4,5,6),SIMPLIFY=FALSE) print(A); str(A) X[1]<-99 print(A) Could someone could comment on what 'force' actually does. I am unclear why force(A) in the code above in the pace of str(A) did not have the effect I expected, whereas str(b) or str(A) did have that effect. > a<-list(c(1,2),c(3,4),c(5,6)) > b<-a[2:3]; force(b) [[1]] [1] 3 4 [[2]] [1] 5 6 > a[[2]][2]<-9 > print(b[[1]][2]) [1] 9 #---------- > X<-1+1 > f<-function(a,b) X > A<-mapply(f,c(1,2,3),c(4,5,6),SIMPLIFY=FALSE) > print(A); force(A) [[1]] [1] 2 [[2]] [1] 2 [[3]] [1] 2 [[1]] [1] 2 [[2]] [1] 2 [[3]] [1] 2 > X[1]<-99 > print(A) [[1]] [1] 99 [[2]] [1] 99 [[3]] [1] 99 > Similar bugs exist in eapply, rapply, and vapply. > -- David Winsemius Alameda, CA, USA ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
