c# - Linq to return ALL pairs of elements from two lists?

Question

Given lists l1 = {1, 2} and l2 = {4, 5, 6 } I want to get a new list that has elements:

rez = { {1, 4}, {1, 5}, {1, 6}, {2, 4}, {2, 5}, {2, 6} }

Suggestions?

Answer 1

Yes it is possible. Eric Lippert wrote a very good article on this topic:

Computing a Cartesian Product with LINQ

If you only have 2 lists, then you could directly use multiple from like this:

from a in s1 
from b in s2 
select new [] { a, b};

or even:

s1.SelectMany(a => s2.Select(b => new [] { a, b }));

But the solution given by Eric Lippert in the previous article allows you to compute the cartesian product of several sequences. With the following extension method:

public static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences)
{
    IEnumerable<IEnumerable<T>> emptyProduct = new[] { Enumerable.Empty<T>() };
    return sequences.Aggregate(
        emptyProduct,
        (accumulator, sequence) =>
        from accseq in accumulator
        from item in sequence
        select accseq.Concat(new[] { item }));
}

You could write:

var l1 = new[] {1, 2};
var l2 = new[] {4, 5, 6};
var l3 = new[] {7, 3};

foreach (var result in new []{l1,l2,l3}.CartesianProduct())
{
    Console.WriteLine("{"+string.Join(",",result)+"}");
}

And obtain:

{1,4,7}
{1,4,3}
{1,5,7}
{1,5,3}
{1,6,7}
{1,6,3}
{2,4,7}
{2,4,3}
{2,5,7}
{2,5,3}
{2,6,7}
{2,6,3}