code: function vertexIdsFromArray(arr)
      {
          var numVertices = arr.length;
          var vertexIds = [];
  
          for(var i = 0; i < numVertices; i++)
          {
              vertexIds.push(arr[i].id);
          }
  
          return vertexIds;
      }
docs: Extracts the vertexIDs from a given array of vertices
  
  @private
  @param {Array} arr - Array of vertices
  @returns {Array}