[Rd] Possible bug in 'relist()' and/or 'as.relistable()'

[Simon Urbanek]

On Apr 14, 2011, at 5:13 PM, Janko Thyson wrote:

> Dear list,
> 
> I think I just stumbled across a bug in either 'relist()' and/or
> 'as.relistable()'. It seems that 'pairlists' can only be un- and relisted as
> long as they're not nested:
> 
> Good:
> a <- as.relistable(as.pairlist(list(a=1, b=2)))
> a <- unlist(a)
> relist(a)# Works
> 
> Bad:
> a <- as.relistable(as.pairlist(list(a=1, b=2, c=list(c.1=1, c.2=2))))

Technically, you're not nesting pairlists - you' are putting a generic vector in a parilist ... (not that it matters here).


> a <- unlist(a)
> relist(a)
> 

relist() has no method for pairlists - but you can actually use the "list" method as-is:

> relist.pairlist <- utils:::relist.list
> str(src <- as.pairlist(list(a=1, b=2, c=list(c.1=1, c.2=2))))
Dotted pair list of 3
 $ a: num 1
 $ b: num 2
 $ c:List of 2
  ..$ c.1: num 1
  ..$ c.2: num 2
> str(relist(unlist(as.relistable(src))))
Dotted pair list of 3
 $ a: num 1
 $ b: num 2
 $ c:List of 2
  ..$ c.1: num 1
  ..$ c.2: num 2
 - attr(*, "class")= chr [1:2] "relistable" "pairlist"

and that will also support actual nested pairlists:

> str(src <- pairlist(a=1, b=2, c=pairlist(c.1=1, c.2=2)))
Dotted pair list of 3
 $ a: num 1
 $ b: num 2
 $ c:Dotted pair list of 2
  ..$ c.1: num 1
  ..$ c.2: num 2
> str(relist(unlist(as.relistable(src))))
Dotted pair list of 3
 $ a: num 1
 $ b: num 2
 $ c:Dotted pair list of 2
  ..$ c.1: num 1
  ..$ c.2: num 2
 - attr(*, "class")= chr [1:2] "relistable" "pairlist"


so I guess it should be easy to add relist.pairlist to utils ... I'm not sure about the implications, but it does sound appealing.

Cheers,
Simon



> The help page didn't say anything about pairlists and I don't know if
> they're at all relevant, but I'm using them whenever I want my functions to
> recognize a clear 'name-value' structure (e.g. for batch assigning
> variables) as opposed to standard list structures.
> 
> Cheers,
> Janko
> 
>>    sessionInfo()
> R version 2.12.1 (2010-12-16)
> Platform: i386-pc-mingw32/i386 (32-bit)
> 
> locale:
> [1] LC_COLLATE=German_Germany.1252  LC_CTYPE=German_Germany.1252   
> [3] LC_MONETARY=German_Germany.1252 LC_NUMERIC=C                   
> [5] LC_TIME=German_Germany.1252    
> 
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base     
> 
> loaded via a namespace (and not attached):
> [1] codetools_0.2-8 tools_2.12.1
> 
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