v.category: add JSON support

[kritibirda26]

Add JSON support to v.category module. The JSON output looks like this:

[
    {
        "type": "line",
        "field": 1,
        "count": 1379,
        "min": 1,
        "max": 1379
    },
    {
        "type": "all",
        "field": 1,
        "count": 1379,
        "min": 1,
        "max": 1379
    }
]

[cwhite911]

@kritibirda26 let's change the output when the action parameter is set to print to return json. The action=print description is the the following

print category values, layers are separated by '|', more cats in the same layer are separated by '/'

Here is a proposed data schema.

{
    "categories": [
          {
                "cat": 1,
                "layers": [
                         {
                              "id": 1,
                              "additional_cats": []
                         }
                   ],
          }
     ]
}

[kritibirda26]

@cwhite911 should I use cat as key name or category? I have used category in r.category module.

[kritibirda26]

@cwhite911 I think that format would be wrong because / represent additional categories in the same layer, not different layers. Also, for the cat value, which category value should be assigned to it? The first category value of the first layer?

{
  "layers": [
     {
        "layer": 1,
        "categories": [
                {
                      "cat": 1,
                      "additional_cats": [2, 3] 
                }
        ],
     }
  ]
}

What do you think?

[echoix]

Is the cat key used uniformly across the JSON PRs (vs category)?

[kritibirda26]

IIRC it is cat except for 1 PR.

[cwhite911]

The option print does not respect the format. Add a test case for option="print", format="json".

It can return an array of category numbers.

{
   "categories": [1,2,3,4,5,..]
}

[cwhite911]

The same should be done when the option is set to layers.