Probability to observe the same number calling Random.Rand()

It’s not an efficient query. Just a game…

for (int j = 1; j < 8; j++)

{

    int numElements = (int)Math.Pow(10, j);

    var numersList = Enumerable.Repeat(0, numElements).Select(

        i => Convert.ToDouble(random.Next()))

        .Distinct().OrderBy(i => i);

    double probabilityGetSameNumber = 1 - (double) numersList.Count()/numElements;

    Console.WriteLine(

        "Rand() was called {0} times. Same number was observed in {1} % cases",

        numElements, probabilityGetSameNumber);

}

Results:

Num of Rand() calls	Same number observed in % of cases	Cases count
10	0	0
100	0	0
1000	0	0
10000	0	0
100000	0.00002999999999997	3
1000000	0.00024100000000004	241
10000000	0.00234760000000001	23476

 

Technorati Теги: C#,Rand(),probability,LINQ