获取对象数组中所有指定元素的总和答案

【问题标题】：Get the sum of all specified elements in an array of objects获取对象数组中所有指定元素的总和
【发布时间】：2017-09-23 12:33:28
【问题描述】：

我有一个对象数组如下

[
    {"width":128.90663423245883,"height":160,"X":0,"Y":140},
    {"width":277.0938568683375,"height":263,"X":128.90663423245883,"Y":37},
    {"width":264.8267031014369,"height":261,"X":277.0938568683375,"Y":39},
    {"width":229.14003389179788,"height":60,"X":264.8267031014369,"Y":240},
    {"width":10.032771905968888,"height":177,"X":229.14003389179788,"Y":123}
]

我正在寻找一个函数来获取当前对象中所有“宽度”元素的总和。

类似：

function getAllBefore(current) {
    // here i want to get the sum of the previous 4 'width' elements in the object
}
getAllBefore(obj[5]);

【问题讨论】：

标签： javascript arrays object multidimensional-array

【解决方案1】：

function count(stack) {
    var totWidth = 0;
    stack.forEach(function(element) {
      totWidth = totWidth+element.width;
    });
  return totWidth;
}

工作example

【讨论】：

【解决方案2】：

如果您在不知道元素索引但只想发送对象的情况下寻找解决方案，那么您需要检查当前项目的所有属性以及可用项目，您可以这样做：

var items = [
{"width":128.90663423245883,"height":160,"X":0,"Y":140},
{"width":277.0938568683375,"height":263,"X":128.90663423245883,"Y":37},
{"width":264.8267031014369,"height":261,"X":277.0938568683375,"Y":39},
{"width":229.14003389179788,"height":60,"X":264.8267031014369,"Y":240},
{"width":10.032771905968888,"height":177,"X":229.14003389179788,"Y":123}
];

function getAllBefore(current) {
    var sum = 0;

    for (var i = 0; i < items.length; i++) {
        var item = items[i];
        if (current.width == item.width && current.height == item.height && current.X == item.X && current.Y == item.Y)
        {
             return sum;
        }

        sum += item.width;
    }
}

getAllBefore(items[2]);

【讨论】：

【解决方案3】：

让我们在 JavaScript 中使用reduce

var arr = [
    {"width":128.90663423245883,"height":160,"X":0,"Y":140},
    {"width":277.0938568683375,"height":263,"X":128.90663423245883,"Y":37},
    {"width":264.8267031014369,"height":261,"X":277.0938568683375,"Y":39},
    {"width":229.14003389179788,"height":60,"X":264.8267031014369,"Y":240},
    {"width":10.032771905968888,"height":177,"X":229.14003389179788,"Y":123}
];

console.log(arr.reduce((acc, b) => acc + b.width, 0.0));

【讨论】：

【解决方案4】：

这是一个示例，使用切片首先返回具有正确长度的数组，然后使用 reduce 来返回总和

const getSum = (objNum, arr) => {
  const newArr =  arr.slice(0, objNum - 1)
  return newArr.reduce((current, next) => {
    return current + next.width;
  }, 0)
}

在 ES5 中

var getSum = (objNum, arr) => {
  vat newArr =  arr.slice(0, objNum - 1)
  return newArr.reduce(function(current, next) {
    return current + next.width;
  }, 0)
}

在 1 行

const getSum = (objNum, arr) => arr.slice(0, objNum - 1).reduce((current, next) =>  current + next.width, 0)

【讨论】：

【解决方案5】：

为了更容易和更可重用的代码传递给方法对象和索引，如下：

function getAllBefore(obj, index){
  var sum=0;
  for(var i=0; i<index; i++){
    sum+=obj[i].width;
  }

  return sum;
}

然后这样称呼它：

getAllBefore(obj, 5);

【讨论】：