I have this code:

IEnumerable<Product> productSelection = from product in products.... select product;

where products.... I want to specify which indexes that are to be selected. Is it SelectMany that I should use? And if so, how would I specify that it's index 0-2 I want to select. Or how would you go about to solve my problem?

have you tried

Element or ElementAt ? 

 I think you need to use the alternate linq syntax (the correct name escapes me at the moment).  There is an overload of the Where operator which works with the index.  Something like

IEnumerable<Product> productSelection  = products.Where((p,n)=> n <= 2);

In this overload of the Where operator the 'p' is each product and 'n' is the index of the product.

Hope that helps

If you're trying to implement paging w/ linq to sql or entity framework use:

var selection = products.Where(...).Skip(pageIndex * pageSize).Take(pageSize);

The other two solutions will perform the full query and filter the indexes on the app-server where as linq to sql will emit sql to only bring back the results you want which will perform much better.

I ended up using this code:


// Specify which indexes to include
int[] IndexesToInclude = new int[] {0,1,4,5,6};
List<Product> filteredProducts = new List<Product>();
foreach(int i in IndexesToInclude)
  if(i < products.Count()) filteredProducts.Add(products.ToArray()[i]);

It would be a good idea to take the products.ToArray() out of the loop.  There is no need to do it every time you go around the loop.  Alternatively,

int[] indexesToInclude = new int[] {0,1,4,5,6};
IEnumerable<Product> filtered = products
                                              .Where((p,n)=> indexesToInclude.Contains(n));