set index(index: Immutable.List<T_SK> | Array<T_SK>) {
    this.set_axis(0, parseIndex(index, this._data.get(this.columns.get(0)).values));

    // noinspection Eslint
    this._data.mapEntries(([k, v]) => { // noinspection Eslint
      v.index = this.index;
    });
  }
Set the index values of the `DataFrame`

@param {List|Array} index
 Next index values

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

// Returns List [0, 1, 2, 3]
df.index;
df.index = Immutable.List([2, 3, 4, 5]);
// Returns List [2, 3, 4, 5]
df.index;