How do I sort an array of objects in reverse order efficiently?

Question

Suppose I have an array of dictionaries:

[ { "id": 2 }, { "id": 59 }, { "id": 31 } ... ]

How can I sort this so that it's in descending order, sorted by "id"?

My initial approach is something like:

Loop through each element, find the biggest one, and put it into a new array. Then, remove that from the element. Repeat.

But I know that's wrong and not efficient.

Possible duplicate of [Swift how to sort array of custom objects by property value](http://stackoverflow.com/questions/24130026/swift-how-to-sort-array-of-custom-objects-by-property-value) — Thilo, Apr 20 '16 at 04:39
There's a ton of sort related information [here](http://stackoverflow.com/questions/24101718/swift-performance-sorting-arrays) — ryantxr, Apr 20 '16 at 04:39

score 6 · Accepted Answer · answered Apr 20 '16 at 04:39

6

You can use the sort function in Swift. Something like this:

let arr = [["id": 2], ["id": 59], ["id": 31]]
let sortedArr = arr.sort { Int($0["id"]!) > Int($1["id"]!) }

answered Apr 20 '16 at 04:39

Ishan Handa

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Thanks Rage. What if It's not [String: Int], but instead it's a custom object (In my case, a message), and it has a property of "id" ? – TIMEX Apr 20 '16 at 04:41
2

just use $0.propertyName instead of $0["id"]. It should work fine. – Ishan Handa Apr 20 '16 at 04:42
1

check the link provided by Thilo. the gave the same link in comments for your question for custom object sorting. – srv_sud Apr 20 '16 at 04:46
`arr.sort{$0.0["id"] > $0.1["id"] }` – Leo Dabus Apr 20 '16 at 04:46
if it was a simple array, you can use the built it sort func: `arr.sort(by: >)` https://apple.co/2FqkBLl – zaxy78 Mar 10 '18 at 18:41

Maheshwar Ligade · Answer 2 · 2016-04-20T05:43:43.673

1

You have only need to use below code that will give you the sorted array using the sort because dictionary is also a collection class.

let sortedDict = wordDict.sort { $0.0 < $1.0 }
print("\(sortedDict)") //

In above code you found the sorted Dictionary. For sorting Array you need to add below code.

let sortedArr = arr.sort { Int($0["id"]!) > Int($1["id"]!) }

edited Apr 20 '16 at 05:43

answered Apr 20 '16 at 04:45

Maheshwar Ligade

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Andrea · Answer 3 · 2016-04-20T04:48:28.027

I don't know if it is the fastest or the better,but swift provides the sort method that takes a clojure as an argument. You can write something like that:

var ordered = arrdict.sort { (dic1, dic2) -> Bool in
    dic1["id"] > dic2["id"]
}

Or compact:

var ordered = arrdict.sort { $0["id"] > $1["id"] }

The $0..x makes possible to access clojure arguments.
About sort algorithm Apple write:

Discussion The sorting algorithm is not stable (can change the relative order of elements that compare equal).

Requires: The less-than operator (func <) defined in the Comparable conformance is a strict weak ordering over the elements in self.

score 0 · Answer 4 · answered Apr 20 '16 at 05:33

    var val = [ { "id": 2 }, { "id": 59 }, { "id": 31 }];
var a = new Array();


for (i = 0; i < val.length; i++) { 
    document.write(Object.keys(val[i]).map(function (key) {return val[i][key]})+"<br>");
    a.push(Object.keys(val[i]).map(function (key) {return val[i][key]}));
}
a.sort();

var result = new Array();
for (i = 0; i < val.length; i++) { 
result.push({"id": a[i]});
}

How do I sort an array of objects in reverse order efficiently?

4 Answers4