R devel - Mar 2013 - Bugs due to naive copying of list elements

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])

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)

Similar bugs exist in eapply, rapply, and vapply.

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

Thanks for the report. Fixed in r62220 on trunk, r62221 on
R-3-0-branch, and r62222 on R-2-15-branch.

Best,

luke

On Tue, 12 Mar 2013, 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])
>
> 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)
>
> Similar bugs exist in eapply, rapply, and vapply.
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
-- 
Luke Tierney
Chair, Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:   luke-tierney at uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu