按数组中的对象分组最有效的方法是什么？
例如，给定此对象数组：
[
{ Phase: "Phase 1", Step: "Step 1", Task: "Task 1", Value: "5" },
{ Phase: "Phase 1", Step: "Step 1", Task: "Task 2", Value: "10" },
{ Phase: "Phase 1", Step: "Step 2", Task: "Task 1", Value: "15" },
{ Phase: "Phase 1", Step: "Step 2", Task: "Task 2", Value: "20" },
{ Phase: "Phase 2", Step: "Step 1", Task: "Task 1", Value: "25" },
{ Phase: "Phase 2", Step: "Step 1", Task: "Task 2", Value: "30" },
{ Phase: "Phase 2", Step: "Step 2", Task: "Task 1", Value: "35" },
{ Phase: "Phase 2", Step: "Step 2", Task: "Task 2", Value: "40" }
]
我正在表格中显示这些信息。我想通过不同的方法进行分组，但我想对值求和。
我将Undercore.js用于其groupby函数，这很有用，但并不能完成全部任务，因为我不希望它们“拆分”，而是“合并”，更像SQL groupby方法。
我要找的是能够合计特定值（如果需要）。
因此，如果我按阶段分组，我希望收到：
[
{ Phase: "Phase 1", Value: 50 },
{ Phase: "Phase 2", Value: 130 }
]
如果我组了阶段/步骤，我会收到：
[
{ Phase: "Phase 1", Step: "Step 1", Value: 15 },
{ Phase: "Phase 1", Step: "Step 2", Value: 35 },
{ Phase: "Phase 2", Step: "Step 1", Value: 55 },
{ Phase: "Phase 2", Step: "Step 2", Value: 75 }
]
是否有一个有用的脚本，或者我应该坚持使用Undercore.js，然后遍历生成的对象，自己计算总数？
具有排序功能
export const groupBy = function groupByArray(xs, key, sortKey) {
return xs.reduce(function(rv, x) {
let v = key instanceof Function ? key(x) : x[key];
let el = rv.find(r => r && r.key === v);
if (el) {
el.values.push(x);
el.values.sort(function(a, b) {
return a[sortKey].toLowerCase().localeCompare(b[sortKey].toLowerCase());
});
} else {
rv.push({ key: v, values: [x] });
}
return rv;
}, []);
};
示例：
var state = [
{
name: "Arkansas",
population: "2.978M",
flag:
"https://upload.wikimedia.org/wikipedia/commons/9/9d/Flag_of_Arkansas.svg",
category: "city"
},{
name: "Crkansas",
population: "2.978M",
flag:
"https://upload.wikimedia.org/wikipedia/commons/9/9d/Flag_of_Arkansas.svg",
category: "city"
},
{
name: "Balifornia",
population: "39.14M",
flag:
"https://upload.wikimedia.org/wikipedia/commons/0/01/Flag_of_California.svg",
category: "city"
},
{
name: "Florida",
population: "20.27M",
flag:
"https://upload.wikimedia.org/wikipedia/commons/f/f7/Flag_of_Florida.svg",
category: "airport"
},
{
name: "Texas",
population: "27.47M",
flag:
"https://upload.wikimedia.org/wikipedia/commons/f/f7/Flag_of_Texas.svg",
category: "landmark"
}
];
console.log(JSON.stringify(groupBy(state,'category','name')));
我从underscore.js fiddler那里借用了这个方法
window.helpers=(function (){
var lookupIterator = function(value) {
if (value == null){
return function(value) {
return value;
};
}
if (typeof value === 'function'){
return value;
}
return function(obj) {
return obj[value];
};
},
each = function(obj, iterator, context) {
var breaker = {};
if (obj == null) return obj;
if (Array.prototype.forEach && obj.forEach === Array.prototype.forEach) {
obj.forEach(iterator, context);
} else if (obj.length === +obj.length) {
for (var i = 0, length = obj.length; i < length; i++) {
if (iterator.call(context, obj[i], i, obj) === breaker) return;
}
} else {
var keys = []
for (var key in obj) if (Object.prototype.hasOwnProperty.call(obj, key)) keys.push(key)
for (var i = 0, length = keys.length; i < length; i++) {
if (iterator.call(context, obj[keys[i]], keys[i], obj) === breaker) return;
}
}
return obj;
},
// An internal function used for aggregate "group by" operations.
group = function(behavior) {
return function(obj, iterator, context) {
var result = {};
iterator = lookupIterator(iterator);
each(obj, function(value, index) {
var key = iterator.call(context, value, index, obj);
behavior(result, key, value);
});
return result;
};
};
return {
groupBy : group(function(result, key, value) {
Object.prototype.hasOwnProperty.call(result, key) ? result[key].push(value) : result[key] = [value];
})
};
})();
var arr=[{a:1,b:2},{a:1,b:3},{a:1,b:1},{a:1,b:2},{a:1,b:3}];
console.dir(helpers.groupBy(arr,"b"));
console.dir(helpers.groupBy(arr,function (el){
return el.b>2;
}));
此解决方案采用任意函数（而不是键），因此比上述解决方案更灵活，并允许箭头函数，这与LINQ中使用的lambda表达式类似：
Array.prototype.groupBy = function (funcProp) {
return this.reduce(function (acc, val) {
(acc[funcProp(val)] = acc[funcProp(val)] || []).push(val);
return acc;
}, {});
};
注意：是否要扩展Array的原型取决于您。
大多数浏览器支持的示例：
[{a:1,b:"b"},{a:1,c:"c"},{a:2,d:"d"}].groupBy(function(c){return c.a;})
使用箭头函数（ES6）的示例：
[{a:1,b:"b"},{a:1,c:"c"},{a:2,d:"d"}].groupBy(c=>c.a)
以上两个示例都返回：
{
"1": [{"a": 1, "b": "b"}, {"a": 1, "c": "c"}],
"2": [{"a": 2, "d": "d"}]
}
