Adding New Group Methods, JavaScript Programming Example of Adding New Group Methods

var chart = webix.ui({
  id:"pivot",
  view:"pivot-chart",
  height:300,
  structure:{
    groupBy: "year",
    values: [{name:"balance", operation:"sum", color: "#eed236"},{name:"balance", operation:"average", color: "#36abee"}],
    filters:[{name:"name", type:"select"}]
  },
  groupMethods:{
    average: function(template, data){
      data = data || this;
      var summ = 0;
      for (var i = 0; i < data.length; i++)
        summ+= template(data[i])*1;
      return data.length?summ/data.length:0;
    }
  },
  data:pivot_data
});