.Net Tips – Use LINQ to avoid nested loops

Admit it, we’ve all done it before, writ­ing those nasty nest­ed loops just so we can iter­ate through mul­ti­ple lists to get some combination/permutation of the lists, e.g.:

   1: for (int i = 0; i < 10; i++)

   2: {

   3:     for (int j = 0; j < 10; j++)

   4:     {

   5:         for (int k = 0; k < 10; k++)

   6:         {

   7:             // do something

   8:         }

   9:     }

  10: }

This code obvi­ous­ly works and well under­stood amongst devel­op­ers, but it’s not very read­able and try­ing to ter­mi­nate the out­er loops from the inner loops is a pain and requires you to use one or more boolean flags which you need to track on every iter­a­tion at poten­tial­ly every lev­el of your loop…

A bet­ter way to solve this com­mon prob­lem is to use LINQ to ‘flat­ten’ the nest­ed loops into a sin­gle loop:

   1: var triplets = from I in Enumerable.Range(0, 10)

   2:                from J in Enumerable.Range(0, 10)

   3:                from K in Enumerable.Range(0, 10)

   4:                select new { I, J, K };

   5:

   6: foreach (var triplet in triplets)

   7: {

   8:     // do something

   9: }

Sweet, right? :-)