/// <summary>
/// Gets an enumerator that enumerates elements of the <see cref="System.Collections.Generic.IEnumerable{T}" /> sequence in a random manner.
/// </summary>
/// <typeparam name="T">The type of elements in the sequence.</typeparam>
/// <param name="sequence">The enumerable sequence.</param>
/// <param name="algorithm">The algorithm used to prevent an element from being accessed twice.</param>
/// <param name="random">A <see cref="System.Random" /> object that generates random numbers.
/// If this argument is not specified, a new <see cref="System.Random" /> instance will be used.</param>
/// <returns>
/// An enumerator that randomly enumerates elements of the sequence.
/// </returns>
public static IEnumerator <T> GetRandomEnumerator <T>(this IEnumerable <T> sequence,
DistinctRandomAlgorithms algorithm = DistinctRandomAlgorithms.Auto, Random random = null)
{
var range = sequence.Count();
var count = range;
if (random == null)
{
random = new Random();
}
switch (algorithm)
{
default:
{
var ratio = (double)count / range;
if (ratio > 0.2)
{
goto case DistinctRandomAlgorithms.Swap;
}
else
{
goto case DistinctRandomAlgorithms.SimpleHash;
}
}
case DistinctRandomAlgorithms.SimpleHash:
{
var hasheset = new HashSet <int>();
while (count != 0)
{
--count;
int val;
do
{
val = random.Next(0, range);
}while (hasheset.Contains(val));
hasheset.Add(val);
yield return(sequence.ElementAt(val));
}
break;
}
case DistinctRandomAlgorithms.Swap:
{
var tempArr = new int[range];
int val;
while (count != 0)
{
val = random.Next(0, range);
--range;
--count;
if (tempArr[val] == 0)
{
yield return(sequence.ElementAt(val));
}
else
{
yield return(sequence.ElementAt(tempArr[val]));
}
tempArr[val] = tempArr[range] == 0 ? range : tempArr[range];
}
break;
}
case DistinctRandomAlgorithms.SwapHash:
{
var dict = new Dictionary <int, int>();
int val;
while (count != 0)
{
val = random.Next(0, range);
--range;
--count;
int tval1, tval2;
var exist1 = dict.TryGetValue(val, out tval1);
var exist2 = dict.TryGetValue(range, out tval2);
if (exist1)
{
dict[val] = exist2 ? tval2 : range;
yield return(sequence.ElementAt(tval1));
}
else
{
dict.Add(val, exist2 ? tval2 : range);
yield return(sequence.ElementAt(val));
}
}
break;
}
}
}
/// <summary>
/// Gets an enumerator that enumerates all elements of the array in a random manner.
/// </summary>
/// <typeparam name="T">The type of elements in the array.</typeparam>
/// <param name="array">The array.</param>
/// <param name="algorithm">The algorithm used to prevent an element from being accessed twice.</param>
/// <param name="random">A <see cref="System.Random" /> object that generates random numbers.
/// If this argument is not specified, a new <see cref="System.Random" /> instance will be used.</param>
/// <returns>
/// An enumerator that randomly enumerates elements of the array.
/// </returns>
public static IEnumerator <T> GetRandomEnumerator <T>(this T[] array,
DistinctRandomAlgorithms algorithm = DistinctRandomAlgorithms.Auto, Random random = null)
{
return(GetRandomEnumerator <T>(array, array.Length, algorithm, random));
}
/// <summary>
/// Gets an enumerator that enumerates all elements of the <see cref="System.Collections.Generic.IList{T}"/> in a random manner.
/// </summary>
/// <typeparam name="T">The type of elements in the list.</typeparam>
/// <param name="array">The list.</param>
/// <param name="algorithm">The algorithm used to prevent an element from being accessed twice.</param>
/// <param name="random">A <see cref="System.Random" /> object that generates random numbers.
/// If this argument is not specified, a new <see cref="System.Random" /> instance will be used.</param>
/// <returns>
/// An enumerator that randomly enumerates elements of the list.
/// </returns>
public static IEnumerator <T> GetRandomEnumerator <T>(this IList <T> list,
DistinctRandomAlgorithms algorithm = DistinctRandomAlgorithms.Auto, Random random = null)
{
return(GetRandomEnumerator <T>(list, list.Count, algorithm, random));
}
/// <summary>
/// Gets an enumerator that enumerates elements of the array in a random manner.
/// </summary>
/// <typeparam name="T">The type of elements in the array.</typeparam>
/// <param name="array">The array.</param>
/// <param name="count">The total number of elements the enumerator should enumerate before reset.</param>
/// <param name="algorithm">The algorithm used to prevent an element from being accessed twice.</param>
/// <param name="random">A <see cref="System.Random" /> object that generates random numbers.
/// If this argument is not specified, a new <see cref="System.Random" /> instance will be used.</param>
/// <returns>An enumerator that randomly enumerates elements of the array.</returns>
public static IEnumerator <T> GetRandomEnumerator <T>(this T[] array, int count,
DistinctRandomAlgorithms algorithm = DistinctRandomAlgorithms.Auto, Random random = null)
{
var range = array.Length;
if (random == null)
{
random = new Random();
}
switch (algorithm)
{
default:
{
var ratio = (double)count / range;
if (ratio > 0.2)
{
goto case DistinctRandomAlgorithms.Swap;
}
else
{
goto case DistinctRandomAlgorithms.SimpleHash;
}
}
case DistinctRandomAlgorithms.SimpleHash:
{
var hasheset = new HashSet <int>();
while (count != 0)
{
--count;
int val;
do
{
val = random.Next(0, range);
}while (hasheset.Contains(val));
hasheset.Add(val);
yield return(array[val]);
}
break;
}
case DistinctRandomAlgorithms.Swap:
{
var tempArr = new int[range];
int val;
var length2 = count; //max is used to store "length" here
while (count != 0)
{
val = random.Next(0, range);
--range;
--count;
if (tempArr[val] == 0)
{
yield return(array[val]);
}
else
{
yield return(array[tempArr[val]]);
}
tempArr[val] = tempArr[range] == 0 ? range : tempArr[range];
}
break;
}
case DistinctRandomAlgorithms.SwapHash:
{
var dict = new Dictionary <int, int>();
int val;
while (count != 0)
{
val = random.Next(0, range);
--range;
--count;
int tval1, tval2;
var exist1 = dict.TryGetValue(val, out tval1);
var exist2 = dict.TryGetValue(range, out tval2);
if (exist1)
{
dict[val] = exist2 ? tval2 : range;
yield return(array[tval1]);
}
else
{
dict.Add(val, exist2 ? tval2 : range);
yield return(array[val]);
}
}
break;
}
}
}
