Compound Select using lambda expression

Question

What is equivalent of following code snippet in lambda expression?

int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 };
int[] numbersB = { 1, 3, 5, 7, 8 };

var pairs =
    from a in numbersA
    from b in numbersB
    where a < b
    select new { a, b };

Just fired up ILSpy to find out, but it didn't change it into methods. (Looks like i'll have to wait for @Jon Skeet!) — George Duckett
– George Duckett, Commented Aug 25, 2011 at 9:44

Martin Liversage · Accepted Answer · 2011-08-25 10:00:46Z

10

Here is a LINQ expression using method syntax (as opposed to query syntax):

int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; 
int[] numbersB = { 1, 3, 5, 7, 8 }; 

pairs = numbersA
  .SelectMany(_ => numbersB, (a, b) => new { a, b })
  .Where(x => x.a < x.b);

The original query is translated into this:

int[] numbersA = { 0, 2, 4, 5, 6, 8, 9 }; 
int[] numbersB = { 1, 3, 5, 7, 8 }; 

pairs = numbersA
  .SelectMany(_ => numbersB, (a, b) => new { a, b })
  .Where(x => x.a < x.b)
  .Select(x => new { x.a, x.b });

However the last Select isn't required and can be removed.

edited Aug 25, 2011 at 10:00

answered Aug 25, 2011 at 9:50

Martin Liversage

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4 Comments

George Duckett Over a year ago

+1, Is that actually what it's translated to, or is that just how you would do it?

Martin Liversage Over a year ago

@George Duckett: I have expanded my answer to answer your comment.

George Duckett Over a year ago

Thanks, out of interest, how did you find out the original translation?

Martin Liversage Over a year ago

I knew that having multiple from translates into SelectMany but I wasn't exactly sure about the last Select so I compated the generated IL and saw it was the same.

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