使用reduce对对象数组求和返回NaN

Question

我有类似于以下代码：

var temp = [ { "y": 32 }, { "y": 60 }, { "y": 60 } ];
var reduced = temp.reduce(function(a, b) {
  return a.y + b.y;
});

console.log(reduced); // Prints NaN

为什么它打印出NaN而不是152？

- Akhilesh Kumar

---

解释这个问题 - 当你返回第一个数后，变量 a 的类型将会是一个数字(Number) - 它没有 y 属性。 - Jaromanda X

检查 reduce 函数的回调参数，它们是什么？ - passion

这个回答解决了你的问题吗？Javascript 对象数组的 reduce - Sebastian Simon

Answer 1

您可以使用起始值，然后仅从数组中添加一个值。

var temp=[{"name":"Agency","y":32,"drilldown":{"name":"Agency","categories":["APPS & SI","ERS"],"data":[24,8]}},{"name":"ER","y":60,"drilldown":{"name":"ER","categories":["APPS & SI","ERS"],"data":[7,53]}},{"name":"Direct","y":60,"drilldown":{"name":"Direct","categories":["APPS & SI","ERS"],"data":[31,29]}}];

var reduced = temp.reduce(function (r, a) {
        return r + a.y;
        //    ^^^ use the last result without property
    }, 0);
//   ^^^ add a start value
console.log(reduced) // r

- Nina Scholz

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一行代码 const reduced = temp.length ? temp.reduce((r, a) => { return r + a.y; }, 0) : 0; - webmaster

@网站管理员，更短的写法是对于空数组，它采用reduce的起始值：const reduced = temp.reduce((r, { a }) => r + a, 0); - Nina Scholz

Answer 2

简单解决方案：将集合映射为整数集合，然后将其缩减。

var temp=[{"name":"Agency","y":32,"drilldown":{"name":"Agency","categories":["APPS & SI","ERS"],"data":[24,8]}},{"name":"ER","y":60,"drilldown":{"name":"ER","categories":["APPS & SI","ERS"],"data":[7,53]}},{"name":"Direct","y":60,"drilldown":{"name":"Direct","categories":["APPS & SI","ERS"],"data":[31,29]}}];

var reduced = temp
                .map(function(obj) { return obj.y; })
                .reduce(function(a, b) { return a + b; });

console.log(reduced);

- Chen