Question

I am trying to use random function in C# to randomly pick four from an array addetailsID which has over six elements.

I am placing these randomly picked into an another array strAdDetailsID:

 string[] strAdDetailsID = new string[4];
 for (int i = 0; i < 4; i++)
 {
     Random random = new Random();
     int index = random.Next(0, addetailsID.Length);
     value = addetailsID[index].ToString();
     strAdDetailsID[i] = value;
 }

Sometimes, I get two of the same values from the six elements. How can I get all four unique values to be picked?

Answer 1

You need to generate 4 unique indices first, then pull the random values from the source array:

        string[] addetailsID = new string[20];  // this is the array I want to index into
        // generate the 4 unique indices into addetailsID
        Random random = new Random();
        List<int> indices = new List<int>();
        while (indices.Count < 4)
        {
            int index = random.Next(0, addetailsID.Length);
            if (indices.Count == 0 || !indices.Contains(index))
            {
                indices.Add(index);
            }
        }
        // now get the 4 random values of interest
        string[] strAdDetailsID = new string[4];
        for (int i = 0; i < indices.Count; i++)
        {
            int randomIndex = indices[i];
            strAdDetailsID[i] = addetailsID[randomIndex];
        }