Sorting Objects by value not working as expected

Question

I'm trying to sort 2 objects based on value.first_name. One ascending alphabetical order. The other descending alphabetical order. However, they are both sorting decending. What am I doing wrong? The goal is to arrange the objects in this array based on the value of first_name.

var participants = [
  {
    id: "992543",
    first_name: "",
    last_name: "",
    company: null,
    notes: "",
    registrationType: "",
    alerts: [ ],
    reg_scan: null
  },
  {
    id: "999070",
    first_name: "Tori",
    last_name: "Fullard",
    company: null,
    notes: "",
    registrationType: "Staff",
    alerts: [ ],
    reg_scan: null
  },
  {
    id: "99265",
    first_name: "Ronald",
    last_name: "Brown",
    company: null,
    notes: "",
    registrationType: "Dean's Guest",
    alerts: [ ],
    reg_scan: null
  },
  {
    id: "992279",
    first_name: "Laila",
    last_name: "Shetty",
    company: null,
    notes: "",
    registrationType: "Table Guest",
    alerts: [
      {
        alert_id: "1",
        dismissed: "0"
      }
    ],
    reg_scan: null
    },
    {
    id: "992248",
    first_name: "Paul",
    last_name: "Keenan",
    company: null,
    notes: "",
    registrationType: "Table Guest",
    alerts: [ ],
    reg_scan: null
    }
    ];

var az_part = participants;
var za_part = participants;
az_part.sort(function(a, b) {
    var nameA = a.first_name.toLowerCase();
    var nameB = b.first_name.toLowerCase();
    if (nameA > nameB) return 1;
    if (nameA < nameB) return -1;
    return 0;
});

za_part.sort(function(a, b) {
    var nameA = a.first_name.toLowerCase();
    var nameB = b.first_name.toLowerCase();
    if (nameA > nameB) return -1;
    if (nameA < nameB) return 1;
    return 0;
});

az_part and za_part are the SAME thing, participants. There is only one array, so you're sorting that same array twice. Check participants and you'll see that it's also sorted the same way even though your code doesn't explicitly sort it. You need to copy the array (participants.slice(0) will do it - you don't particularly need a deep-copy here) — Niet the Dark Absol
– Niet the Dark Absol, Commented Apr 26, 2017 at 18:03

apsillers · Accepted Answer · 2017-04-26 18:03:22Z

3

All three variables az_part, za_part, and participants refer to the exact same array in memory. You are transforming that one array with an ascending sort and then immediately re-sorting it with a descending sort.

Use slice to create shallow copies of the array:

var az_part = participants.slice();
var za_part = participants.slice();

(By "shallow copy" I mean that this will create a new list, but it will not create new objects. Each resulting list will be different -- and can be sorted differently -- but if you mutate any of the objects inside, e.g., participants[2].notes = "foo", that will change the object as it exists in each list.)

answered Apr 26, 2017 at 18:03

apsillers

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Community · Accepted Answer · 2017-05-23 11:54:35Z

0

JavaScript objects (including arrays) are references to objects. So you're sorting the original array twice.

see this question for a good description of your problem.

Why does changing an Array in JavaScript affect copies of the array?

edited May 23, 2017 at 11:54

CommunityBot

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answered Apr 26, 2017 at 18:14

Stuart H.

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