[R] reading json tables

[Duncan Temple Lang]

Hi Michael

  The problem is that the content of the .js file is not JSON,
but actual JavaScript code.

You could use something like the following

tt = readLines("http://mbostock.github.com/protovis/ex/wheat.js")

txt = c("[", gsub(";", ",", gsub("var [a-zA-Z]+ = ", "", tt)), "]")
tmp = paste(txt, collapse = "\n")
tmp = gsub("([a-zA-Z]+):", '"\\1":', tmp)
o = fromJSON(tmp)
data = structure(o[1:2], names = c("wheat", "monarch"))

Basically, this
    removes the 'var <variable name> =' part
    replaces the ; with a , to separate elements
    quotes the names of the fields, e.g. year, wheat, wages
    puts the two global data objects into a top-level array ([]) container

This isn't ideal (as the regular expressions are not sufficiently specific
and could modify the actual values incorrectly). However, it does the job
for this particular file.

On 12/1/12 12:47 PM, Michael Friendly wrote:
> I'm trying to read two data sets in json format from a single .js file. I've tried fromJSON()
> in both RJSONIOIO and RJSON packages, but they require that the lines be
> pre-parsed somehow in ways I don't understand.  Can someone help?
> 
>> wheat <- readLines("http://mbostock.github.com/protovis/ex/wheat.js")
>> str(wheat)
>  chr [1:70] "var wheat = [" "  { year: 1565, wheat: 41, wages: 5 }," ...
>>
> 
> The wheat.js file looks like this and defines two tables:  wheat and monarch:
> 
> var wheat = [
>   { year: 1565, wheat: 41, wages: 5 },
>   { year: 1570, wheat: 45, wages: 5.05 },
>   { year: 1575, wheat: 42, wages: 5.08 },
>   { year: 1580, wheat: 49, wages: 5.12 },
>   { year: 1585, wheat: 41.5, wages: 5.15 },
>   { year: 1590, wheat: 47, wages: 5.25 },
>   { year: 1595, wheat: 64, wages: 5.54 },
>   { year: 1600, wheat: 27, wages: 5.61 },
>   { year: 1605, wheat: 33, wages: 5.69 },
>   { year: 1610, wheat: 32, wages: 5.78 },
>   { year: 1615, wheat: 33, wages: 5.94 },
>   { year: 1620, wheat: 35, wages: 6.01 },
> ...
>   { year: 1800, wheat: 79, wages: 28.5 },
>   { year: 1805, wheat: 81, wages: 29.5 },
>   { year: 1810, wheat: 99, wages: 30 },
>   { year: 1815, wheat: 78 }, // TODO
>   { year: 1820, wheat: 54 },
>   { year: 1821, wheat: 54 }
> ];
> 
> var monarch = [
>   { name: "Elizabeth", start: 1565, end: 1603 },
>   { name: "James I", start: 1603, end: 1625 },
>   { name: "Charles I", start: 1625, end: 1649 },
>   { name: "Cromwell", start: 1649, end: 1660, commonwealth: true },
>   { name: "Charles II", start: 1660, end: 1685 },
>   { name: "James II", start: 1685, end: 1689 },
>   { name: "W&M", start: 1689, end: 1702 },
>   { name: "Anne", start: 1702, end: 1714 },
>   { name: "George I", start: 1714, end: 1727 },
>   { name: "George II", start: 1727, end: 1760 },
>   { name: "George III", start: 1760, end: 1820 },
>   { name: "George IV", start: 1820, end: 1821 }
> ];
>