Assign characteristics to particular items within an array

When working with AngularJS/Javascript, I have an array of objects that each contain a date. My goal is to order these objects by date and then add an attribute to the last object that has a specific datetime. If there are two objects with the same date, the attribute should be added to the one with the latest time. If there is only one object with a particular date, then the attribute should be added to that object.

For example:

input:   var arr = [
          {A: {"Date": "2017-08-14T15:15:00"} B:{}}
          {A: {"Date": "2017-08-14T16:15:00"} B:{}} //<--- Add attribute to this object 
         ] 

output:  var arr = [
          {A: {"Date": "2017-08-14T15:15:00"} B:{}}
          {A: {"Date": "2017-08-14T16:15:00"} B:{} C:{"NewAttribute": "true"}}
         ]

I am unsure how to approach programming this. Initially, I thought about using a for loop to compare all the objects, but I'm stuck on how to implement it.

javascriptangularjsarrays

Answer №1

It seems like I have understood your requirement:

var data = [
  {A: {"Date": "2017-08-14T15:15:00"}, B:{}}, // will not receive the new property
  {A: {"Date": "2017-08-14T16:12:00"}, B:{}}, // will receive the new property
  {A: {"Date": "2017-08-14T15:15:00"}, B:{}}, // will receive the new property
  {A: {"Date": "2017-08-14T16:14:00"}, B:{}}, // won't get the new property
  {A: {"Date": "2017-08-14T16:14:00"}, B:{}}  // will receive the new property
];

// sort the array by date in descending order
var sortedData = data.sort(({A: { Date: d1 }}, {A: { Date: d2 }}) => new Date(d2).getTime() - new Date(d1).getTime());

// add the new property as required
sortedData.reduce((acc, obj) => {
  var dateValue = obj.A.Date;
  if (acc !== dateValue) {
    obj.C = {"NewAttribute": "true"};
  }
  return dateValue;
}, '');

// reverse the array
var finalResult = sortedData.slice().reverse();

console.log(finalResult);

Answer №2

To start, it is recommended to arrange the array based on the date by utilizing Array.prototype.sort(). After sorting, you can proceed to add a new attribute to the final element:

let array = [
      {A: {"Date": "2017-08-14T15:15:00"},B: {}},
      {A: {"Date": "2017-08-16T16:15:00"},B: {}},
      {A: {"Date": "2017-08-24T16:15:00"},B: {}},
      {A: {"Date": "2017-08-24T16:15:00"},B: {}, C: {}}
    ],
    alphaArray = 'abcdefghijklmnopqrstuvwxyz'
      .toUpperCase()
      .split(''),
    lastItemLength = 0;

// Sorting the array
array.sort(function (x, y) {
  return new Date(y.A.date) - new Date(x.A.date);
});

// Determining the length of properties in the last element
lastItemLength = Object.keys(array[array.length - 1]).length;

// Adding a new attribute to the last element with an appropriate name
array[array.length - 1][alphaArray[lastItemLength]] = {
  "NewAttribute": "true"
};

console.log(array);
.as-console-wrapper { max-height: 100% !important; top: 0; }

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