Better way to sort array in descending order

Question

I have a array of int which I have to sort by descending.

Since I did not find any method to sort the array in descending order.Currently I am sorting the array in descending order as below

int[] array = new int[] { 3, 1, 4, 5, 2 };
Array.Sort<int>( array );
Array.Reverse( array );

Now,the question is that.Is there any better way to do the same in c#?

If there is no huge constraint on time, I would stick with Array.Sort followed by Array.Reverse. Reason is readability is very high, and asymptotically, Array.Reverse() is simply a O(n) operation. — user3613932, Jul 10 '19 at 16:40

score 75 · Answer 1 · answered Mar 25 '11 at 08:25

75

Use LINQ OrderByDescending method. It returns IOrderedIEnumerable<int>, which you can convert back to Array if you need so. Generally, List<>s are more functional then Arrays.

array = array.OrderByDescending(c => c).ToArray();

answered Mar 25 '11 at 08:25

Ilya Smagin

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This is a short working code, but if the array is large, it is not very efficient (in performance term), because the array is converted to list first, then sorted, and finally converted to array. Am I wrong ? – JYL Mar 25 '11 at 09:14
@Ilyusha, If consider `int` from perspective of composite objects (not simple objects), then `int` it's the same object like others, because either of two objects you need to compare till 1st difference, so O(n) it's impossible result. – Kirill Polishchuk Jun 29 '11 at 15:28
Google translate of @Ilyusha's (which I still don't fully understand): Integers can be sorted in O (n). There is a view in a very low level, the number represented by a sequence of bits. Then, technically, to compare two numbers require fewer resources than the reading of two of them. This suggests an unusual way as the storage and comparing, so sisyarpe about this there can be no question. – zod Aug 15 '12 at 08:27
@JYL You're not wrong. `OrderBy()` is a different algorithm than `Array.Sort()`. Anyone interested see this post https://stackoverflow.com/questions/1832684/c-sharp-sort-and-orderby-comparison – Kellen Stuart Nov 20 '21 at 04:11

score 72 · Accepted Answer · answered Mar 25 '11 at 08:23

72

Depending on the sort order, you can do this :

    int[] array = new int[] { 3, 1, 4, 5, 2 };
    Array.Sort<int>(array,
                    new Comparison<int>(
                            (i1, i2) => i2.CompareTo(i1)
                    ));

... or this :

    int[] array = new int[] { 3, 1, 4, 5, 2 };
    Array.Sort<int>(array,
                    new Comparison<int>(
                            (i1, i2) => i1.CompareTo(i2)
                    ));

i1 and i2 are just reversed.

answered Mar 25 '11 at 08:23

JYL

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This, or just add a `-` (minus sign) before `CompareTo` – digEmAll Mar 25 '11 at 08:31
22

Or simply `Array.Sort(array, (a, b) => b.CompareTo(a))` for a reverse sort. – Matthew Strawbridge Nov 06 '14 at 12:04
3

true, but sometimes slower… so it depends what you want and what you sort, see: http://stackoverflow.com/questions/6842090/fastest-way-to-sort-an-array-in-descending-order – v01pe Sep 10 '15 at 08:02
Or do this: 'Array.Sort(array, (i1,i2) => i2.CompareTo(i1))' – Muhammad Yasir Oct 09 '17 at 14:06

Yochai Timmer · Answer 3 · 2016-06-03T20:49:56.280

11

Sure, You can customize the sort.

You need to give the Sort() a delegate to a comparison method which it will use to sort.

Using an anonymous method:

Array.Sort<int>( array,
delegate(int a, int b)
  {
    return b - a; //Normal compare is a-b
  });

Read more about it:

Sorting arrays
MSDN - Array.Sort Method (T[], Comparison)

edited Jun 03 '16 at 20:49

answered Mar 25 '11 at 08:31

Yochai Timmer

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bear in mind, u might get integer overflow for b - a when b is int.MinValue and a is any positive number. Better always to do b.CompareTo(a) – Daniel B Dec 16 '20 at 23:17

Alex Aza · Answer 4 · 2020-12-16T20:31:44.203

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For in-place sorting in descending order:

int[] numbers = { 1, 2, 3 };
Array.Sort(numbers, (a, b) => b.CompareTo(a));

For out-of-place sorting (no changes to input array):

int[] numbers = { 1, 2, 3 };
var sortedNumbers = numbers.OrderByDescending(x => x).ToArray();

edited Dec 16 '20 at 20:31

answered Mar 14 '20 at 19:51

Alex Aza

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bear that in mind, u might get integer overflow for b - a when b is int.MinValue and a is any positive number. Better always do b.CompareTo(a) – Daniel B Nov 29 '20 at 21:02
@DanielB it's quite an edge case with int overflow, but other than that if you are sure your input data are not of that kind, this is the shortest 1-line code for sorting descending, and should be higher in top answers. – tytyryty Jul 22 '23 at 07:17

score 2 · Answer 5 · answered Mar 25 '11 at 08:24

2

Yes, you can pass predicate to sort. That would be your reverse implementation.

answered Mar 25 '11 at 08:24

Sasha Reminnyi

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score 2 · Answer 6 · answered Mar 25 '11 at 08:24

2

You may specify a comparer(IComparer implementation) as a parameter in Array.Sort, the order of sorting actually depends on comparer. The default comparer is used in ascending sorting

answered Mar 25 '11 at 08:24

Tony Kh

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score 0 · Answer 7 · answered Jan 29 '19 at 09:48

class Program
{
    private static int[] table;

    static void Main(string[] args)
    {
        int[] ints = new int[] { 6, 2, 5, 99, 55 };

       table = ints.OrderByDescending(x => x).ToArray();

        foreach (var item in table)
        {
            Console.WriteLine(item);
        }

    }

Better way to sort array in descending order

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