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？
如果您需要通过以下方式进行多组：
const populate = (entireObj, keys, item) => {
let keysClone = [...keys],
currentKey = keysClone.shift();
if (keysClone.length > 0) {
entireObj[item[currentKey]] = entireObj[item[currentKey]] || {}
populate(entireObj[item[currentKey]], keysClone, item);
} else {
(entireObj[item[currentKey]] = entireObj[item[currentKey]] || []).push(item);
}
}
export const groupBy = (list, key) => {
return list.reduce(function (rv, x) {
if (typeof key === 'string') (rv[x[key]] = rv[x[key]] || []).push(x);
if (typeof key === 'object' && key.length) populate(rv, key, x);
return rv;
}, {});
}
const myPets = [
{name: 'yaya', type: 'cat', color: 'gray'},
{name: 'bingbang', type: 'cat', color: 'sliver'},
{name: 'junior-bingbang', type: 'cat', color: 'sliver'},
{name: 'jindou', type: 'cat', color: 'golden'},
{name: 'dahuzi', type: 'dog', color: 'brown'},
];
// run
groupBy(myPets, ['type', 'color']));
// you will get object like:
const afterGroupBy = {
"cat": {
"gray": [
{
"name": "yaya",
"type": "cat",
"color": "gray"
}
],
"sliver": [
{
"name": "bingbang",
"type": "cat",
"color": "sliver"
},
{
"name": "junior-bingbang",
"type": "cat",
"color": "sliver"
}
],
"golden": [
{
"name": "jindou",
"type": "cat",
"color": "golden"
}
]
},
"dog": {
"brown": [
{
"name": "dahuzi",
"type": "dog",
"color": "brown"
}
]
}
};
发帖是因为即使这个问题已经7年了，我仍然没有看到一个符合原始标准的答案：
我不希望它们“拆分”，而是“合并”，更像SQL组方法
我最初发表这篇文章是因为我想找到一种方法来减少对象数组（例如，当您从csv中读取时创建的数据结构），并通过给定索引聚合以生成相同的数据结构。我正在寻找的返回值是另一个对象数组，而不是我在这里看到的嵌套对象或映射。
下面的函数获取一个数据集（对象数组）、一个索引列表（数组）和一个reducer函数，并将reducer功能应用于索引的结果作为一个对象数组返回。
function agg(data, indices, reducer) {
// helper to create unique index as an array
function getUniqueIndexHash(row, indices) {
return indices.reduce((acc, curr) => acc + row[curr], "");
}
// reduce data to single object, whose values will be each of the new rows
// structure is an object whose values are arrays
// [{}] -> {{}}
// no operation performed, simply grouping
let groupedObj = data.reduce((acc, curr) => {
let currIndex = getUniqueIndexHash(curr, indices);
// if key does not exist, create array with current row
if (!Object.keys(acc).includes(currIndex)) {
acc = {...acc, [currIndex]: [curr]}
// otherwise, extend the array at currIndex
} else {
acc = {...acc, [currIndex]: acc[currIndex].concat(curr)};
}
return acc;
}, {})
// reduce the array into a single object by applying the reducer
let reduced = Object.values(groupedObj).map(arr => {
// for each sub-array, reduce into single object using the reducer function
let reduceValues = arr.reduce(reducer, {});
// reducer returns simply the aggregates - add in the indices here
// each of the objects in "arr" has the same indices, so we take the first
let indexObj = indices.reduce((acc, curr) => {
acc = {...acc, [curr]: arr[0][curr]};
return acc;
}, {});
reduceValues = {...indexObj, ...reduceValues};
return reduceValues;
});
return reduced;
}
我将创建一个返回count（*）和sum（Value）的reducer：
reducer = (acc, curr) => {
acc.count = 1 + (acc.count || 0);
acc.value = +curr.Value + (acc.value|| 0);
return acc;
}
最后，使用我们的reducer将agg函数应用于原始数据集会生成一个应用了适当聚合的对象数组：
agg(tasks, ["Phase"], reducer);
// yields:
Array(2) [
0: Object {Phase: "Phase 1", count: 4, value: 50}
1: Object {Phase: "Phase 2", count: 4, value: 130}
]
agg(tasks, ["Phase", "Step"], reducer);
// yields:
Array(4) [
0: Object {Phase: "Phase 1", Step: "Step 1", count: 2, value: 15}
1: Object {Phase: "Phase 1", Step: "Step 2", count: 2, value: 35}
2: Object {Phase: "Phase 2", Step: "Step 1", count: 2, value: 55}
3: Object {Phase: "Phase 2", Step: "Step 2", count: 2, value: 75}
]
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"}]
}
