Custom Visualization additional DataViewCategoryColumn

Hello,

I'm trying to develop a custom visual that replicates an arc chart for every existing category. I've used the source code of a waffle chart that can be found in github (which I cannot link because the post will be tagged as spam), and I'm on the right path:

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However, I'm unable to configure a DataViewCategoryColumn for the second level of categories (The slices of the arc chart). 

In the current code, I can set up the first categories: 

 public static converter(dataView: DataView): PieChartViewModel {
            var labelsArray: Array<string> = [];
            var arcsArray: Array<string> = [];
            var Arcs: DataViewCategoryColumn;
            var category0: DataViewCategoryColumn;
            //matrix.columns.root.children
            if (dataView.categorical.categories && dataView.categorical.categories.length > 0) { let categories = dataView.categorical.categories;  category0 = categories[0];
                var rowsCount = category0.values.length;
                labelsArray = [];
                arcsArray = [];
                for (let i = 0; i < rowsCount; i++) {
                    let labelPieces: Array<string> = [];
                    for (let j = 0; j < categories.length; j++) {
                        labelPieces.push(this.formatCategoryValue(categories[j].values[i], categories[j].source.type));
                    }
                    labelsArray.push(labelPieces.join("|"));
                }
                var sliceCount = dataView.categorical.values.grouped();
                //.values["0"].__proto__.source.groupName
                for(let j=0; j<sliceCount.length; j++){
                    console.log(sliceCount[j].values[0]["__proto__"].source.groupName);
                    arcsArray.push(this.formatCategoryValue(sliceCount[j].values[0]["__proto__"].source.groupName, sliceCount[j].values[0]["__proto__"].source.type));
                }
           }

However, I'm unable to find a node from which I could set up a similar object for the second dimension of categories. I could create a new array but I believe I need to use the right object type and I'm struggling to do so.

Currently, my dataViewMappings look like this:

   cappabilities.json

"dataViewMappings": [
        {
            "conditions": [
                {
                    "Category": {
                        "min": 0,
                        "max": 3
                    },
                    "Paths": {
                        "min": 0,
                        "max": 1
                    },
                    "Values": {
                        "min": 0,
                        "max": 1
                    },
                    "Measure": {
                        "min": 0,
                        "max": 1
                    }
                }
            ],
            "categorical": {
                "categories": {
                    "for": { 
                        "in": "Category"
                    },
                    "dataReductionAlgorithm": { 
                        "top": {}
                    }
                },
                "values": {
                    "group": {
                        "by": "Paths",
                        "select":[
                            {
                               "for":{
                                  "in":"Values"
                               }
                            }
                         ], 
                        "dataReductionAlgorithm": {
                            "top": {}
                        }
                    }
                }
            }
        }

Could you please give me a clue?

Thanks a lot in advance!
Guillermo