Getting odd/even part of a sequence with LINQ
c#, linq
Solution
If you're using LINQ to SQL or LINQ to Entities you should first fully materialize the results into memory:
var oddCategories = projectsByCat.ToList().Where((c,i) => i % 2 != 0);
var evenCategories = projectsByCat.ToList().Where((c,i) => i % 2 == 0);
It isn't possible to iterate through results on the database with an indexer without the use of a cursor, which either ORM framework does not do.
Problem
Say I have a list of all `Projects`, and that I group them by `Category` like this: ``` var projectsByCat = from p in Projects group p by p.Category into g orderby g.Count() descending select new { Category = g.Key, Projects = g }; ``` Now I want to display this as a list in a web page, where first I create the left side div, secondly the right side div. I am ordering by number of `Projects` in each `Category` to show the `Categories` with the most `Projects` on top - thus I would like to split `projectsByCat` in two - if I put all the "odd numbered" `Categories` on the left and the "even numbered" categories on the right, I think I will get a reasonably sane view. So I thought I could do this to get the odd and even members of `projectsByCat`: ``` var oddCategories = projectsByCat.Where((cat, index) => index % 2 != 0); var evenCategories = projectsByCat.Where((cat, index) => index % 2 == 0); ``` And it compiles - however, when I run it, I get an exception such as this: Unsupported overload used for query operator 'Where'. And I thought I was safe since it compiled in the first place.. ;) Is there an elegant way to do this? And also, is there an elegant explanation for why my creative use of `Where()` won't work?