How to create an extension method that will allow me to call ToSerializableDictionary(p => p.ID) instead of .ToDictionary(p => p.ID)

Question

I would like to create an extension method that will allow me to call ToSerializableDictionary(p => p.ID) instead of .ToDictionary(p => p.ID) in the following LINQ context. Though I'm not sure what class i'm supposed to be making an extension method for to replace ToDictionary<T>.

response.attributes = (
    from granuleGroup in groups
    let granuleRow = granuleGroup.First().First()
    select new USDAttributes()
    {
        id = (int)granuleRow["id"],
        ...
        attributes =
        (
            ...
        ).ToDictionary(p => p.ID) <--** LINE IN QUESTION **
    }
).ToList();

My SerializableDictionary class taken from here is so that I may serialize dictionary objects in my webservice to return hash tables that play nice with JSON.

Initially I was creating an extension method for IDictionary so I can do something like this: ...).ToDictionary(p => p.ID).ToSerializableDictionary(); But this has been a complete failure because it's my first time creating extension methods and I don't know what I'm doing.

public static class CollectionExtensions
{

    public static SerializableDictionary<string, object> ToSerializableDictionary(this IDictionary<string,object> sequence)
    {

        SerializableDictionary<string, object> sDic = new SerializableDictionary<string, object>();


        foreach (var item in sequence)
        {

        }

        return sDic;

    }
}

Answer 1

public static SerializableDictionary<TKey, T> ToSerializableDictionary<TKey, T>(this IEnumerable<T> seq, Func<T, TKey> keySelector)
{
    var dict = new SerializableDictionary<TKey, T>();
    foreach(T item in seq)
    {
        TKey key = keySelector(item);
        dict.Add(key, item);
    }

    return dict;
}

Answer 2

Actually the class you provided has a handy constructor for doing this, so you can actually do

attributes = new SerializableDictionary( (
        ...
    ).ToDictionary(p => p.ID) );

But here you go with the extension method (again using that constructor):

public static partial class Extension {
    public static SerializableDictionary<T, Q> ToSerializableDictionary(
        this IDictionary<T, Q> d) {

        return new SerializableDictionary(d);
    }
}