Transformations inside the 'Marks' don't add the extra_field to data.

[Ellyster]

When you try to use the transformation inside a mark, like this:

data = pdata.name('table') do
  url('data/groups.json')
end

facet_t = facet_transform.keys('category')

group_m = group_mark.from(data, facet_t) do
  enter do
    y { scale(cat_s).field('key') }
  end
end

Because it is not properly adding the transformation new field to data, it generates this:

"marks": [{ 
  "type": "group",
   "from": { "data": "table" },
   "properties": {
      "enter": {
        "y": { "field": "data.key", "scale": "cat"},
      }
    }
  }],

But it actually should be like this:

"marks": [{ 
  "type": "group",
   "from": { "data": "table" },
   "properties": {
      "enter": {
        "y": { "field": "key", "scale": "cat"},
      }
    }
  }],