Select a random item from a weighted list

Question

I am trying to write a program to select a random name from the US Census last name list. The list format is

Name           Weight Cumulative line
-----              


        

Answer 1

The "easiest" way to handle this would be to keep this in a list.

You could then just use:

Name GetRandomName(Random random, List names)
{
    double value = random.NextDouble() * names[names.Count-1].Culmitive;
    return names.Last(name => name.Culmitive <= value);
}

If speed is a concern, you could store a separate array of just the Culmitive values. With this, you could use Array.BinarySearch to quickly find the appropriate index:

Name GetRandomName(Random random, List names, double[] culmitiveValues)
{
    double value = random.NextDouble() * names[names.Count-1].Culmitive;
    int index = Array.BinarySearch(culmitiveValues, value);
    if (index >= 0)
        index = ~index;

    return names[index];
}

Another option, which is probably the most efficient, would be to use something like one of the C5 Generic Collection Library's tree classes. You could then use RangeFrom to find the appropriate name. This has the advantage of not requiring a separate collection