Verify if a user typed a word from a ReactiveList with Reactive Extension - system.reactive

Question

I have a ReactiveList with keywords. The user can add or remove keyword from that list. The app needs to verify if the user typed one of the keywords.
There was already a similar post but it doesn't take in account a flexible list:
Using Reactive Extension for certain KeyPress sequences?
var keyElements = new ReactiveList<KeyElement>();
IObservable<IObservable<int>> rangeToMax = Observable.Merge(keyElements.ItemsAdded, keyElements.ItemsRemoved).Select(obs => Observable.Range(2, keyElements.Select(ke => ke.KeyTrigger.Length).Max()));
IObservable<IObservable<string>> detectedKeyTrigger = rangeToMax
.Select(n => _keyPressed.Buffer(n, 1))
.Merge().Where(m => keyElements.Where(ke => ke.KeyTrigger == m).Any());
//Here I want to end up with IObservable<string> instead of IObservable<IObservable<string>>
I can get rid of the outer IObservable by reassigning the detectedKeyTrigger each time an element in the reactive list changes, but then I lose all my subscriptions.
So, how can I end up with just an Observable of strings?

Answer 1

First off, both Max and Any have overloads which takes a selector and a predicate respectively. This negates the need of the Select.
Next, I changed the Observable.Merge to use the Changed property of ReactiveList which is the Rx version of INotifyCollectionChanged. I also changed the Select to produce an IEnumerable of ints instead; it just felt more Right™.
var keyElements = new ReactiveList<KeyElement>();
IObservable<IEnumerable<int>> rangeToMax = keyElements.Changed
.Select(_ => Enumerable.Range(2, keyElements.Max(keyElement => keyElement.KeyTrigger.Length));
IObservable<IObservable<string>> detectedKeyTrigger = rangeToMax.
.Select(range => range
.Select(length => _keyPressed.Buffer(length, 1).Select(chars => new string(chars.ToArray()))) // 1
.Merge() // 2
.Where(m => keyElements.Any(ke => ke.KeyTrigger == m)) // 3
.Switch(); // 4
Create an IObservable<string> which emits the last n characters typed by the user. Create such an observable for each of the possible lengths of an combo
Merge the observables in the IEnumerable<IObservable<string>> into one Observable<string>
Only let strings which mach one of the KeyTriggers through
As rangeToMax.Select produces an IObservable<IObservable<string>> we use Switch to only subscribe to the most recent IObservable<string> the IObservable<IObservable<string>> produces.