R devel - Sep 2005 - Assigning a zero length vector to a list (PR#8157)

Full_Name: Jussi Jousimo
Version: 2.2.0 beta
OS: Windows XP
Submission from: (NULL) (193.167.195.60)


I'm trying to assign a zero length vector to a list:

x<-numeric()
length(x)
foo<-list()
foo$bar[[1]]<-x
length(foo$bar[[1]])
foo

But in the list this vector turns out to be length one with random content.
x<-character() makes R to crash.

On 9/26/2005 7:34 AM, jussi.jousimo at ktl.fi wrote:
> Full_Name: Jussi Jousimo
> Version: 2.2.0 beta
> OS: Windows XP
> Submission from: (NULL) (193.167.195.60)
> 
> 
> I'm trying to assign a zero length vector to a list:
> 
> x<-numeric()
> length(x)
> foo<-list()
> foo$bar[[1]]<-x
> length(foo$bar[[1]])
> foo
> 
> But in the list this vector turns out to be length one with random content.
> x<-character() makes R to crash.
After foo<-list(), foo$bar is NULL, so we can simplify this.

Here's a simpler version:

# These work, which is a bit of a surprise, but there is some 
inconsistency:   one x becomes a list, the other is numeric:
 > x <- NULL
 > x[[1]] <- 1:10
 > x
[[1]]
  [1]  1  2  3  4  5  6  7  8  9 10

 > x <- NULL
 > x[[1]] <- 1
 > x
[1] 1


# This generates the same bug as the above:
 > x <- NULL
 > x[[1]] <- numeric(0)
 > x
[1] 4.250083e-314

It looks like we're trying to be too clever with handling assignments to 
components of NULL.  Wouldn't it make more sense for those to generate 
an error?

Duncan Murdoch

Duncan Murdoch <murdoch at stats.uwo.ca> writes:
> After foo<-list(), foo$bar is NULL, so we can simplify this.
> 
> Here's a simpler version:
> 
> # These work, which is a bit of a surprise, but there is some 
> inconsistency:   one x becomes a list, the other is numeric:
>  > x <- NULL
>  > x[[1]] <- 1:10
>  > x
> [[1]]
>   [1]  1  2  3  4  5  6  7  8  9 10
> 
>  > x <- NULL
>  > x[[1]] <- 1
>  > x
> [1] 1
> 
> 
> # This generates the same bug as the above:
>  > x <- NULL
>  > x[[1]] <- numeric(0)
>  > x
> [1] 4.250083e-314
> 
> It looks like we're trying to be too clever with handling assignments
to
> components of NULL.  Wouldn't it make more sense for those to generate 
> an error?
Once upon a time, we had pairlists, and NULL was the empty list. This
looks like it might be a relic. If so, it likely also predates
consistent handling of zero-length vectors, so something is getting
confused. I think it would be reasonable to expect similar results to
this: 
> x<-list()
> x[[1]] <- numeric(0)
> x
[[1]]
numeric(0)

 

S-PLUS also tries to handle NULL as a zero length list, with some
anomalies:
> x <- NULL
> x[[1]] <- numeric(0)
> x
$value:
numeric(0)

> x <- list()
> x[[1]] <- numeric(0)
> x
[[1]]:
numeric(0)


-- 
   O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907

On 9/26/2005 10:29 AM, Peter Dalgaard wrote:
> Duncan Murdoch <murdoch at stats.uwo.ca> writes:
> 
>> After foo<-list(), foo$bar is NULL, so we can simplify this.
>> 
>> Here's a simpler version:
>> 
>> # These work, which is a bit of a surprise, but there is some 
>> inconsistency:   one x becomes a list, the other is numeric:
>>  > x <- NULL
>>  > x[[1]] <- 1:10
>>  > x
>> [[1]]
>>   [1]  1  2  3  4  5  6  7  8  9 10
>> 
>>  > x <- NULL
>>  > x[[1]] <- 1
>>  > x
>> [1] 1
>> 
>> 
>> # This generates the same bug as the above:
>>  > x <- NULL
>>  > x[[1]] <- numeric(0)
>>  > x
>> [1] 4.250083e-314
>> 
>> It looks like we're trying to be too clever with handling
assignments to
>> components of NULL.  Wouldn't it make more sense for those to
generate
>> an error?
> 
> Once upon a time, we had pairlists, and NULL was the empty list. This
> looks like it might be a relic. If so, it likely also predates
> consistent handling of zero-length vectors, so something is getting
> confused. I think it would be reasonable to expect similar results to
> this: 
> 
>> x<-list()
>> x[[1]] <- numeric(0)
>> x
> [[1]]
> numeric(0)
I agree.  I think I see where the problem is (a test "length(y) <=
1" in
do_subassign2_dflt in subassign.c should be "length(y) == 1"; I'll
try
to fix it.

Duncan Murdoch
> 
>  
> 
> S-PLUS also tries to handle NULL as a zero length list, with some
> anomalies:
> 
>> x <- NULL
>> x[[1]] <- numeric(0)
>> x
> $value:
> numeric(0)
> 
> 
>> x <- list()
>> x[[1]] <- numeric(0)
>> x
> [[1]]:
> numeric(0)
> 
>