Filter IEnumerable

c#, filtering

Solution

Interesting - it is a little confusing what you're asking here.

I think you're asking how to have `Offers` filtered in-place. If so:

`IEnumerable<T>` is immutable (you have to cast to a concrete `List<T>` or similar to get mutability), and `Offers` is an `IEnumerable<T>` - so you can't expect `Offers.Where(o => !o.IsSealed));` to change the `Offers` property - it returns an enumerable that filters the source as you enumerate it.

Instead you'd do

var offerList = this.GetOfferList(id)
offerList.Offers = offerList.Offers.Where(o => !o.IsSealed));

Note, however, that this hides the original `Offers` reference for any other code sharing that `OfferList` instance. It also doesn't actually do any filtering until you start enumerating, either. But that's often preferable. If you want it done there and then - use `.ToArray()` or `.ToList()` at the end of the `Where` to force the enumeration to be done.

A better approach would be to have a property or method on the `OfferList` class that returns a new enumerable on-demand:

public IEnumerable<Offer> UnsealedOffers {
  get {
    return Offers.Where(o => !o.IsSealed);
  }
}

That way you're not destroying the master enumerable.

Note that this code is susceptible to `Offers` being null (a `NullReferenceException`) and that it's not great to return null enumerables (return empty ones instead) - so if there is a chance that `Offers` can be null - then either stop that from happening; or use:

return (Offers ?? Enumerable.Empty<Offer>()).Where(o => !o.IsSealed);

Problem

I have 3 classes with the following properties: OfferList class: ``` Guid Id IEnumerable<Offer> Offers ``` Offer class: ``` Guid Id Product Product bool IsSealed ``` Product class: ``` Guid Id ``` An OfferList contains multiple Offers and an Offer has exact 1 Product. How can I filter the OfferList to contain only Offers which are not sealed? ``` OfferList offerList = this.GetOfferList(id).Offers.Where(o => !o.IsSealed)); ``` This returns an IEnumerable of type Offer instead of filtering the OfferList.

Original source