Add attribute to specific objects in an array

Question

In AngularJS/Javascript i have an array of objects, these objects contain a date. I want to order these objects by date and add an attribute to the last object with a specific datetime. So if 2 objects have the same date i want to add the attribute to the one with the latest time. If there is only one object with one date i want to add the attribute to that object.

An 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"}} 
         ]

How do i go about programming this? Originally i was thinking about using a for loop to compare all the objects with each other but i have no idea how to implement it.

PeterMader · Accepted Answer · 2017-08-17 10:10:23Z

1

I hope I understood what you want:

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

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

// eventually add the new property
sorted.reduce((acc, o) => {
  var date = o.A.Date;
  if (acc !== date) {
    // the date isn't equal to the date of the last item, so it's
    // either the only item with that date
    // or the first (in reversed order) item with that date
    o.C = {"NewAttribute": "true"};
  }
  return date;
}, '');

// reverse the array
var result = sorted.slice().reverse();

console.log(result);

answered Aug 17, 2017 at 10:10

PeterMader

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2 Comments

A1RStack Over a year ago

It's almost the answer that i'm looking for, however if they have the same date, but not the same timestamp. The attribute needs to be added to the time that is later.

A1RStack Over a year ago

Discard my previous comment. I made an error when using this code. It works thanks!

Yosvel Quintero · Accepted Answer · 2017-08-17 10:49:55Z

0

You can first sort the array by Date using Array.prototype.sort() and than add the new attribute to the last element:

var arr = [
      {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: {}}
    ],
    alphabetArr = 'abcdefghijklmnopqrstuvwxyz'
      .toLocaleUpperCase()
      .split(''),
    lastElementLength = 0;

// Sort the array
arr.sort(function (a, b) {
  return new Date(b.A.date) - new Date(a.A.date);
});

// Get last element properties length
lastElementLength = Object.keys(arr[arr.length - 1]).length;

// Adds new attribute to last element with the proper name..
arr[arr.length - 1][alphabetArr[lastElementLength]] = {
  "NewAttribute": "true"
};

console.log(arr);

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

edited Aug 17, 2017 at 10:49

answered Aug 17, 2017 at 10:03

Yosvel Quintero

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2 Comments

PeterMader Over a year ago

As I understood it, if you have an item ({A: {"Date": "1900-08-14T15:15:00"},B: {}}, for example), which is the only item with that date, it should also get the new property, even if it's not the very last item in the list.

Yosvel Quintero Over a year ago

I understood "add an attribute to the last object with a specific datetime" no matter if at the end where multiple objects with the same datetime

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