调用reduce to sum对象数组返回NaN

Calling reduce to sum array of objects returns NaN

本文关键字：数组 返回 NaN 对象 sum reduce to 调用      更新时间：2023-09-26

我有类似这样的代码:

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

为什么打印NaN而不是152

你可以使用一个起始值，并且只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

简解:将集合映射为整数集合，并约简

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);
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