Get the sum of all specified elements in an array of objects

问题

I have an array of objects as folllows

[
    {"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}
]

I am looking to write a function that gets the sum of all 'width' elements in the object before the current.

Something like:

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

回答1:

For an easier and more reusable code pass to the method the object and the index, as follows:

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

  return sum;
}

And call it like this:

getAllBefore(obj, 5);

回答2:

Here is an example using a slice to first return the array with the correct length and the a reduce to return the sum

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

and in ES5

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

and in 1 line

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

回答3:

Let's use reduce in JavaScript

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));

回答4:

If you are looking for solution without knowing index of element but you want only to send object, then you will need to check all properties of current item with available items and you can do it like this:

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]);

回答5:

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

working example

来源：https://stackoverflow.com/questions/43628549/get-the-sum-of-all-specified-elements-in-an-array-of-objects

标签

javascript

arrays

object

multidimensional-array