How to convert linq results to HashSet or HashedSet

Question

I have a property on a class that is an ISet. I'm trying to get the results of a linq query into that property, but can't figure out how to do so.

Basically, looking for the last part of this:

ISet<T> foo = new HashedSet<T>();
foo = (from x in bar.Items select x).SOMETHING;

Could also do this:

HashSet<T> foo = new HashSet<T>();
foo = (from x in bar.Items select x).SOMETHING;

Edit: This is what I ended up doing:

    public static HashSet<T> ToHashSet<T>(this IEnumerable<T> source)
    {
        return new HashSet<T>(source);
    }

    public static HashedSet<T> ToHashedSet<T>(this IEnumerable<T> source)
    {
        return new HashedSet<T>(source.ToHashSet());
    }

Answer 1

Just pass your IEnumerable into the constructor for HashSet.

HashSet<T> foo = new HashSet<T>(from x in bar.Items select x);

Answer 2

I don't think there's anything built in which does this... but it's really easy to write an extension method:

public static class Extensions
{
    public static HashSet<T> ToHashSet<T>(this IEnumerable<T> source)
    {
        return new HashSet<T>(source);
    }
}

Note that you really do want an extension method (or at least a generic method of some form) here, because you may not be able to express the type of T explicitly:

var query = from i in Enumerable.Range(0, 10)
            select new { i, j = i + 1 };
var resultSet = query.ToHashSet();

You can't do that with an explicit call to the HashSet<T> constructor. We're relying on type inference for generic methods to do it for us.

Now you could choose to name it ToSet and return ISet<T> - but I'd stick with ToHashSet and the concrete type. This is consistent with the standard LINQ operators (ToDictionary, ToList) and allows for future expansion (e.g. ToSortedSet). You may also want to provide an overload specifying the comparison to use.

Answer 3

That's pretty simple :)

var foo = new HashSet<T>(from x in bar.Items select x);

and yes T is the type specified by OP :)

Answer 4

You could just use the IEnumerable HashSet constructor.

HashSet<T> foo = new HashSet<T>((from x in bar.Items select x).ToArray());

Answer 5

As @Joel stated, you can just pass your enumerable in. If you want to do an extension method, you can do:

public static HashSet<T> ToHashSet<T>(this IEnumerable<T> items)
{
    return new HashSet<T>(items);
}

Answer 6

Jon's answer is perfect. The only caveat is that, using NHibernate's HashedSet, I need to convert the results to a collection. Is there an optimal way to do this?

ISet<string> bla = new HashedSet<string>((from b in strings select b).ToArray()); 

or

ISet<string> bla = new HashedSet<string>((from b in strings select b).ToList()); 

Or am I missing something else?