Concatenate 3 lists of words

问题:

I am trying to figure out how to create a single concatenated list using C#, originating from 3 separate lists. For example:

 List 1: Ugly, Pretty
 List 2: Dogs, Carts, Pigs
 List 3: Rock, Suck

Output:

 Ugly Dogs Rock
 Ugly Dogs Suck
 Ugly Cats Rock
 Ugly Cats Suck
 Ugly Pigs Rock
 Ugly Pigs Suck
 Pretty Dogs Rock
 Pretty Dogs Suck
 Pretty Cats Rock
 Pretty Cats Suck
 Pretty Pigs Rock
 Pretty Pigs Suck

I know it is just nested loops, but the part I cant figure out is how to use List-strings for each list.

回答1:

var list = from s1 in list1
           from s2 in list2
           from s3 in list3
           select s1 + " " + s2 + " " + s3;

回答2:

Isn't it a Cartesian product?

var r = from i1 in list1
        from i2 in list2
        from i3 in list3
        select new { i1, i2, i3 };
        // or String.Format("{0} {1} {2}", i1, i2, i3);

回答3:

List<string> list1 = new List<string>(){ "Ugly", "Pretty"};
List<string> list2 = new List<string>(){ "Dogs", "Carts", "Pigs"};
List<string> list3 = new List<string>(){ "Rock", "Suck"};

var result = from s1 in list1
             from s2 in list2
             from s3 in list3
             select new[] { s1, s2, s3 };

foreach (var item in result)
{
    Console.WriteLine(String.Join(",", item));
}

If you are looking for a more general solution, not only for 3 lists you may try Eric Lippert's solution

foreach (var item in new[] { list1, list2, list3 }.CartesianProduct())
{
    Console.WriteLine(String.Join(",", item));
}

---

public static partial class MyExtensions
{
    // Eric Lippert’s Blog
    // Computing a Cartesian Product with LINQ
    // http://blogs.msdn.com/b/ericlippert/archive/2010/06/28/computing-a-cartesian-product-with-linq.aspx
    public static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences)
    {
        // base case: 
        IEnumerable<IEnumerable<T>> result = new[] { Enumerable.Empty<T>() };
        foreach (var sequence in sequences)
        {
            var s = sequence; // don't close over the loop variable 
            // recursive case: use SelectMany to build the new product out of the old one 
            result =
                from seq in result
                from item in s
                select seq.Concat(new[] { item });
        }
        return result;
    }
}