R devel - Jun 2009 - Issues converting from JSON to R

When converting from JSON to R it seems logical that a JSON array would
correspond to an "unnamed" R list, while a JSON object would
correspond to a
"named" R list.  E.g.
JSON: [1, 3.1415927, "foo", false, null]   => R: list(1, 3.1415927,
"foo",
FALSE, NA);

and

JSON { "int": 1, "float": 3.1415927, "string":
"foo", "logical": false,
"null": null }  => R: list(int=1, float=3.1415927,
string="foo",
logical=FALSE, null=NA)

But I see at least a couple of problems with this scheme.  First, how would
one distinguish between the R versions of an empty JSON array (i.e. [ ]),
and an empty JSON object (i.e. { })?

Second, JSON allows the empty key in an object (e.g., this is a valid JSON
object: { "": 123 }), but as far as I can tell, R does not allow the
empty
string as a name in a named list:
> list(""=123)
Error: attempt to use zero-length variable name



Any suggestions for dealing with these edge cases would be much appreciated!

TIA!

kynn

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On Jun 12, 2009, at 6:34 PM, Kynn Jones wrote:
> When converting from JSON to R it seems logical that a JSON array  
> would
> correspond to an "unnamed" R list, while a JSON object would  
> correspond to a
> "named" R list.  E.g.
> JSON: [1, 3.1415927, "foo", false, null]   => R: list(1,
3.1415927,
> "foo",
> FALSE, NA);
>
note that NULL and NA are entirely different concepts - I don't think  
mapping NULL to NA is a good idea ... why don't you just use NULL?

> and
>
> JSON { "int": 1, "float": 3.1415927,
"string": "foo", "logical":
> false,
> "null": null }  => R: list(int=1, float=3.1415927,
string="foo",
> logical=FALSE, null=NA)
>
> But I see at least a couple of problems with this scheme.  First,  
> how would
> one distinguish between the R versions of an empty JSON array (i.e.  
> [ ]),
> and an empty JSON object (i.e. { })?
>
Just add an attribute in that special case for one or the other. Or  
even better in general you can make JSON dictionaries (or arrays as  
well) a specific class (each) -- that would also help with future  
dispatch when processing such objects. Also note that specific arrays  
(scalar ones) are actually better mapped to vectors ...

> Second, JSON allows the empty key in an object (e.g., this is a  
> valid JSON
> object: { "": 123 }), but as far as I can tell, R does not allow
the
> empty
> string as a name in a named list:
>
That's not true, try
l=list(123)
names(l)=""
>> list(""=123)
> Error: attempt to use zero-length variable name
>
That has nothing to do with lists per se - the problem is the empty  
argument name in the call to the function `list`. However, you'll be  
creating the list programmatically so you won't run into that.

Cheers,
Simon

>
>
> Any suggestions for dealing with these edge cases would be much  
> appreciated!
>
> TIA!
>
> kynn
>
> 	[[alternative HTML version deleted]]
>
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