Reading JSON file from R

Question

I try reading a JSON file from R using rjson but keep getting errors. I validated the JSON file using various online validators. Here is the content of the JSON file:

{
   "scenarios": [
      {
         "files": {
            "type1": "/home/blah/Desktop/temp/scen_0.type1",
            "type2": "/home/blah/Desktop/temp/scen_0.type2"
         },
         "ID": "scen_0",
         "arr": [],
         "TypeToElementStatsFilename": {
            "type1": "/home/blah/Desktop/temp/scen_0.type1.elements",
            "type2": "/home/blah/Desktop/temp/scen_0.type2.elements"
         }
      }
   ],
   "randomSeed": "39327314969888",
   "zone": {
      "length": 1000000,
      "start": 1
   },
   "instanceFilename": "/home/blah/bloo/data/XY112.zip",
   "txtFilename": "/home/blah/bloo/data/XY112.txt",
   "nSimulations": 2,
   "TypeTodbFilename": {
      "type1": "/home/blah/bloo/data/map.type1.oneAmb.XY112.out"
   },
   "arr": {
      "seg11": {
         "length": 1000,
         "start": 147000
      },
      "seg12": {
         "length": 1000,
         "start": 153000
      },
      "seg5": {
         "length": 1000,
         "start": 145000
      },
      "seg6": {
         "length": 1000,
         "start": 146000
      },
      "seg1": {
         "length": 100,
         "start": 20000
      }
   },
   "outPath": "/home/blah/Desktop/temp",
   "instanceID": "XY112",
   "arrIds": [
      "seg5",
      "seg6",
      "seg1",
      "seg11",
      "seg12"
   ],
   "truth": {
      "files": {
         "type1": "/home/blah/Desktop/temp/truth.type1",
         "type2": "/home/blah/Desktop/temp/truth.type2"
      },
      "ID": "truth",
      "TypeToElementStatsFilename": {
         "type1": "/home/blah/Desktop/temp/truth.type1.elements",
         "type2": "/home/blah/Desktop/temp/truth.type2.elements"
      }
   }
}

And the error:

> json_file <- "~/json"
> json_data <- fromJSON(paste(readLines(json_file), collapse=""))
Error in fromJSON(paste(readLines(json_file), collapse = "")) :
  unexpected character: :

Answer 1

RJSON freaks out about empty arrays.

fromJSON( '{ "arr": [ ] }')

Error in fromJSON("{ \"arr\": [ ] }") : unexpected character: :

Answer 2

You can try the fromJSON function in the RJSONIO package hosted at http://www.omegahat.org. It seems to read the file fine.