get values(): T_LIST {
    if (this._values instanceof Immutable.List)
      return super.values;

    let valuesList = Immutable.List([]);
    for (let idx = 0; idx < this.length; idx += 1) {
      valuesList = valuesList.concat(
        [Immutable.List(this.columns.map(k => this._data.get(k).iloc(idx)))]);
    }
    this._values = valuesList;

    return super.values;
  }
Immutable.List of Immutable.List, with [row][column] indexing

pandas equivalent: [DataFrame.values](http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.values.html)

@returns {List.<List>}

@example
const df = new DataFrame([{x: 1, y: 2}, {x: 2, y: 3}, {x: 3, y: 4}]);

// Returns List [ List[1, 2, 3], List[2, 3, 4]]
df.values;