static sortByAtomicNumberDesc(arr) {
    let map = arr.map(function (e, i) {
      return {
        index: i,
        value: e.atomicNumber.split('.').map(Number)
      };
    });
    map.sort(function (a, b) {
      let min = Math.min(b.value.length, a.value.length);
      let i = 0;

      while (i < min && b.value[i] === a.value[i]) {
        i++;
      }

      return i === min ? b.value.length - a.value.length : b.value[i] - a.value[i];
    });
    return map.map(function (e) {
      return arr[e.index];
    });
  }
Sort an array of atomic number information. Where the number is indicated as x, x.y, x.y.z, ...

@param {Object[]} arr An array of vertex ids with their associated atomic numbers.
@param {Number} arr[].vertexId A vertex id.
@param {String} arr[].atomicNumber The atomic number associated with the vertex id.
@returns {Object[]} The array sorted by atomic number. Example of an array entry: { atomicNumber: 2, vertexId: 5 }.