Shuffle a Collection

  • Thread starter Thread starter Aamir Mahmood
  • Start date Start date
A

Aamir Mahmood

Hi everyone,

I have to write a function to shuffle a collection. If anyone has any idea
on how to implement it please share with me.

The signature of function is:
ICollection Shuffle(ICollection c);

Thanks.

AM
 
I have already implemented it, any comments/suggestions on my implementation
are welcome:
----------------------------------------------------------------------
public static ICollection Shuffle(ICollection c) {
if (c == null || c.Count <= 1) {
return c;
}

byte[] bytes = new byte[4];
RNGCryptoServiceProvider cRandom = new RNGCryptoServiceProvider();
cRandom.GetBytes(bytes);

int seed = BitConverter.ToInt32(bytes, 0);
Random random = new Random(seed);

ArrayList orig = new ArrayList(c);
ArrayList randomized = new ArrayList(c.Count);
for (int i = 0; i < c.Count; i++) {
int index = random.Next(orig.Count);
randomized.Add(orig[index]);
orig.RemoveAt(index);
}
return randomized;
}
------------------------------------------------



Thanks.

AM
 
Aamir said:
I have to write a function to shuffle a collection. If anyone has any idea
on how to implement it please share with me.

The signature of function is:
ICollection Shuffle(ICollection c);
Click to expand...

2.0+ style:

public class Util<T>
{
private static Random rng = new Random();
public static ICollection<T> Shuffle(ICollection<T> c)
{
T[] a = new T[c.Count];
c.CopyTo(a, 0);
byte[] b = new byte[a.Length];
rng.NextBytes(b);
Array.Sort(b, a);
return new List<T>(a);
}
}

1.x style:

public class Util
{
private static Random rng = new Random();
public static ICollection Shuffle(ICollection c)
{
object[] a = new object[c.Count];
c.CopyTo(a, 0);
byte[] b = new byte[a.Length];
rng.NextBytes(b);
Array.Sort(b, a);
return new ArrayList(a);
}
}

Arne
 
2.0+ style:
Click to expand...

<snip>

Shuffling by sorting is going to be (at best) O(n log n). It's fairly
easy to do it as O(n)... admittedly it's more code, but for large
collections it could be significant.

Jon
 
Jon said:
<snip>

Shuffling by sorting is going to be (at best) O(n log n). It's fairly
easy to do it as O(n)... admittedly it's more code, but for large
collections it could be significant.
Click to expand...

True.

The advantage of the sorting method is that the methods validity
is rather obvious.

Arne
 
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