How to distribute an array to smaller arrays randomly?

Question

I want to create same sized smaller arrays from a big array. But items should distribte randomly. I can distribute by order like following:

int[] source = new[] { 10, 20, 30, 40, 50, 60, 70, 80, 90 };
int i = 0;
int chunkSize = 3;
var result = source.GroupBy(s => i++ / chunkSize).Select(g => g.ToArray()).ToArray();

// [10,20,30][40,50,60][70,80,90]

But result should be random like: // [90,20,50][70,30,60][40,80,10] Can I do it using linq?

The same as what you have, but `OrderBy` before the `GroupBy`. The `OrderBy` should use `Random`. — mjwills, Jul 24 '19 at 13:37
Possible duplicate of [Randomize a List](https://stackoverflow.com/questions/273313/randomize-a-listt) — Guilhem Prev, Jul 24 '19 at 13:38

score 1 · Accepted Answer · answered Jul 24 '19 at 13:47

The following implements the suggestions in the comments to add an OrderBy clause. There are, of course, other ways to achieve the result, but this is likely the simplest way using LINQ, as requested.

int[] source = new[] { 10, 20, 30, 40, 50, 60, 70, 80, 90 };
int i = 0;
int chunkSize = 3;
Random r = new Random();
var result = source.OrderBy(x => r.Next()).GroupBy(s => i++ / chunkSize).Select(g => g.ToArray()).ToArray();

pappbence96 · Answer 2 · 2019-07-24T13:51:28.413

0

You can shuffle any 1D array with this method. If you modify it to return IList<T> instead of void, you can append it into your query:

var result = source.Shuffle().GroupBy(...)

edited Jul 24 '19 at 13:51

answered Jul 24 '19 at 13:39

pappbence96

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The Shuffle has to be done at the beginning of the Linq query not when the array is already cut in parts – Guilhem Prev Jul 24 '19 at 13:45
1

I don't really see any problems with that either. Just do `var result = source.Shuffle().GroupBy(...)`. – pappbence96 Jul 24 '19 at 13:46
Your first method random the small part of the rule. It will be [20, 30, 10], [40, 60, 50] ... The OP want a random at the beginning – Guilhem Prev Jul 24 '19 at 13:48
Yeah, that's right, I'm gonna edit my comment into my answer. – pappbence96 Jul 24 '19 at 13:50

score 0 · Answer 3 · answered Jul 24 '19 at 14:02

You could do the following.

var arr = new int[] { 1, 1, 2, 6, 6, 7, 1, 1, 0 };
var sizeOfResultArray = 3;
var result  = arr.ChunkBy(sizeOfResultArray);

The extension methods are defined as

public static class Extensions
{

    private static Random rng = new Random();  
    public static IEnumerable<IEnumerable<T>> ChunkBy<T>(this IEnumerable<T> source, int chunkSize) 
    {
        return source.Shuffle()
            .Select((x, i) => new { Index = i, Value = x })
            .GroupBy(x => x.Index / chunkSize)
            .Select(x => x.Select(v => v.Value).ToList())
            .ToList();
    }
    public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> list)  
    {  
        var collection = list.ToList();
        int n = collection.Count();
        while (n > 1) 
        {  
            n--;  
            int k = rng.Next(n + 1);  
            T value = collection[k];  
            collection[k] = collection[n];  
            collection[n] = value;  
        } 
        return collection;
    }
}

The Shuffle is a Fisher-Yates shuffle implementation by Grenade here

score -1 · Answer 4 · answered Jul 24 '19 at 13:45

-1

You need to randomize and then group. Code below should work

            int[] source = new[] { 10, 20, 30, 40, 50, 60, 70, 80, 90 };
            Random rand = new Random();
            int[] random = source.Select(x => new { num = x, rand = rand.Next() }).OrderBy(x => x.rand).Select(x => x.num).ToArray();
            int groupsize = 3;
            int[][] groups = random.Select((x, i) => new { num = x, index = i })
                .GroupBy(x => x.index / groupsize)
                .Select(x => x.Select(y => y.num).ToArray())
                .ToArray();

answered Jul 24 '19 at 13:45

jdweng

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No. To sort you need array of pairs {10, 12}, {20, 4} {30, 7} {40, 8} {50, 3} {60, 5} {70, 3} {80, 55} {90, 20} – jdweng Jul 24 '19 at 13:57
https://dotnetfiddle.net/dIStUh might be an example of what I mentioned. – mjwills Jul 24 '19 at 14:05

How to distribute an array to smaller arrays randomly?

4 Answers4