使用sum对JavaScript数组分组

var array = [{t_id:"1",val1:"1",title:"cash to purchase",unit:"bag"},{t_id:"1",val1:"1",title:"cash to purchase",unit:"bag"},{t_id:"1",val1:"1",title:"cash to purchase",unit:"bag"},{t_id:"2",val1:"4",title:"offload",unit:"bag"},{t_id:"2",val1:"5",title:"onroad",unit:"bag"},{t_id:"3",val1:"5",title:"Onroad",unit:"bag"},{t_id:"3",val1:"6",title:"Onroad",unit:"bag"}];


var grouped = [];

array.forEach(function(o) {
  var count = 0;
  if (!this[o.t_id]) {
    this[o.t_id] = {
      t_id: o.t_id,
      val1: 0,
      title: o.title,
      counter: count
    };
    grouped.push(this[o.t_id]);
  }
  this[o.t_id].val1 += Number(o.val1);
  this[o.t_id].counter += Number(++count);
}, Object.create(null));

console.log(grouped);

var sources = [
{t_id: "1", val1: "1", title: "cash to purchase", unit: "bag"},
{t_id: "1", val1: "1", title: "cash to purchase", unit: "bag"},
{t_id: "1", val1: "1", title: "cash to purchase", unit: "bag"},
{t_id: "2", val1: "4", title:"offload", unit :"bag"},
{t_id: "2", val1: "5", title:"onroad", unit :"bag"},
{t_id: "3", val1: "5", title:"Onroad", unit :"bag"},
{t_id: "3", val1: "6", title:"Onroad", unit :"bag"}
];

var groups = {};
for(var i in sources){
	var source = sources[i];
	if(typeof groups[source.t_id] !== 'undefined'){
    	groups[source.t_id].sum_of_val1 += Number(source.val1);
    	groups[source.t_id].num_of_items += 1;
    }else{
    	groups[source.t_id] = source;
        groups[source.t_id].sum_of_val1 = Number(source.val1);
    	groups[source.t_id].num_of_items = 1;
    }
}

// print out put
for(var i in groups){
	var group = groups[i];
	
    document.write("Title: " + group.title + "<br/>Bag: " + (group.sum_of_val1 / group.num_of_items) + " (ie.: " + group.sum_of_val1 + " / " + group.num_of_items+ ")<br/><br/>");
}