gistfile1.cs

IObservable<IDictionary<string, bool>> ValidateManyUrisAsync(string[] Uris)
{
    // Aggregate will take a "future list" and return a future with only one item
    // (Just like LINQ's Aggregate takes a list and returns a single value)

    // For every result that ValidateUrlAsync provides, we will execute the
    // Aggregate block. When SelectMany completes, Aggregate can finally
    // return its one result 

    return Uris.ToObservable()
       .SelectMany(x => ValidateUriAsync(x))
       .Aggregate(new ConcurrentDictionary<string, bool>(), (acc, pair) => {
           acc.TryAdd(pair.Key, pair.Value);
           return acc;
       });
}