CODEWITHSUNDEEP
c#.netlinq
Cristian Diaconescu
Cristian Diaconescu

Reputation: 35621

Linq to return ALL pairs of elements from two lists?

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?

Upvotes: 23

Views: 11213

Answers (7)

Graham Clark
Graham Clark

Reputation: 12966

Eric Lippert's already done it for you!

http://blogs.msdn.com/b/ericlippert/archive/2010/06/28/computing-a-cartesian-product-with-linq.aspx

you probably just want to the linq fluent syntax of SelectMany

var s1 = new[] {a, b}; 
var s2 = new[] {x, y, z}; 


var product = 
from first in s1 
from second in s2 
select new[] { first, second };

product.SelectMany(o=>o);

or Eric's blog post version

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; 
}

product.CartesianProduct();

Upvotes: 4

Romain Verdier
Romain Verdier

Reputation: 12971

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}

Upvotes: 44

Cristian Diaconescu
Cristian Diaconescu

Reputation: 35621

Great article by Eric Lippert - see links in other answers. What's even better, this was the first try I did before looking at the answers on this page :)

In short:

var rez = 
    from e1 in l1
    from e2 in l2 
    select new {e1, e2};

Upvotes: 2

NetSide
NetSide

Reputation: 3890

Here you go; 

var rez =  from first in l1 
           from second in l2 
           select new[] { first, second };

Upvotes: 2

cirons42
cirons42

Reputation: 74

something like this will do what you are looking for.

var l1 = new List<int>{1,2};
var l2 = new List<int>{4,5,6};

var p = from n in l1
        from m in l2
        select new { Fst = n, Scd = m };

with this answer your tuples {x,y} are an anonymous type.

Upvotes: 1

Justin Niessner
Justin Niessner

Reputation: 245399

var result = from a in l1
             from b in l2
             select new[] { a, b }

Upvotes: 3

Jader Dias
Jader Dias

Reputation: 90465

You want

l1.Join(l2, a => 1, b => 1, (a, b) => new [] { a, b });

Upvotes: -3

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