Get random items with fixed length of different types

Question

I have a List<Fruit>,

public class Fruit
{
    public string Name { get; set; }
    public string Type { get; set; }
}

and the list above contains 30 Fruit objects of two types: Apple and Orange. 20 apples and 10 oranges.

List<Fruit> fruits = new List<Fruit>();
fruits.Add(new Fruit(){ Name = "Red Delicious", Type = "Apple" });
fruits.Add(new Fruit(){ Name = "Granny Smith", Type = "Apple" });
fruits.Add(new Fruit(){ Name = "Sour Granny", Type = "Orange" });
fruits.Add(new Fruit(){ Name = "Delicious Yummy", Type = "Orange" });
.....

How can I get a list of 10 random fruits (from the basket of 30 fruits), but there should be 3 oranges and 7 apples?

Answer 1

You can use LINQ and Guid or Random to make a random selection:

var apples = fruits.
     Where( f => f.Type == "Apple" ). //choose only from apples
     OrderBy( f => Guid.NewGuid() ). //order randomly
     Take( 7 ). //take 7 apples
     ToList();

The same goes for oranges, just with "Orange" instead of "Apple" and with 3 instead of 7.

How does it work?

OrderBy sorts the enumerable by the given condition. Because Guid.NewGuid() returns a random unique identifier, the result is that the items are ordered randomly. When we then apply Take( n ), it will take the n first items in this random order.

Note that instead of Guid you can create an instance of Random and the use f => random.NextDouble() as the OrderBy expression. This is potentially a safer solution, because Guid.NewGuid() is not guaranteed to be random, only to be unique.