Add usage examples for reactive operators

[banchan86]

Partially addresses bonsai-rx/roadmap#15

Progress

100/100 Bonsai.Reactive operators reviewed
The examples have been updated with the VisualizerWindow from Bonsai 2.9.0
Click on operator link for online preview - some might not be up yet till I update the demo branch.:

Operators covered with examples

Operator	Category	Basic Example	Application Examples	Alternatives
Accumulate	Quantitative	✓		Sum
Average	Quantitative	✓	Signal Smoothing
Count	Quantitative	✓		ElementIndex
Min	Quantitative	✓
Max	Quantitative	✓
Scan	Quantitative	✓		Accumulate
Sum	Quantitative	✓		Accumulate
CombineLatest	Combine	✓	Video Synchronization	WithLatestFrom
Concat	Combine	✓	Stimulus Composition	Merge OnErrorResumeNext
Merge	Combine	✓	Input Aggregation	Zip CombineLatest WithLatestFrom Concat
WithLatestFrom	Combine	✓	Video Synchronization Background Subtraction	CombineLatest
Zip	Combine	✓	Combine Processing Results Combine Related Events Sample Preloaded Sequences	WithLatestFrom CombineLatest
Gate	Dynamic Filter	✓		GateInterval WindowTrigger BufferTrigger
Sample	Dynamic Filter	✓		SampleInterval Zip
SkipUntil	Dynamic Filter	✓	Start Video Recording	SubscribeWhen
SubscribeWhen	Dynamic Filter	✓		SkipUntil
TakeUntil	Dynamic Filter	✓	Stop Video Recording
Condition	Filter	✓
Distinct	Filter	✓		DistinctUntilChanged
DistinctUntilChanged	Filter	✓	Signal State Transitions
First	Filter	✓		Take FirstOrDefault
FirstOrDefault	Filter	✓		Take
Last	Filter	✓		TakeLast LastOrDefault
LastOrDefault	Filter	✓		TakeLast
Slice	Filter	✓	Deinterleave Video Frames	GateInterval
Skip	Filter	✓	Discard Startup Elements	Slice
SkipLast	Filter	✓		Delay
SkipWhile	Filter	✓		SkipUntil Condition
Take	Filter	✓		First
TakeLast	Filter	✓		Last
TakeWhile	Filter	✓		TakeUntil Condition
Timer	Element Generation	✓
Range	Element Generation	✓
CreateTimestamped	Temporal	*
Delay	Temporal	✓		DelaySubscription
DelaySubscription	Temporal	✓		Delay
GateInterval	Temporal	✓		SampleInterval Slice Gate
SampleInterval	Temporal	✓		GateInterval Slice Sample
Throttle	Temporal	*
TimeInterval	Temporal	✓
Timestamp	Temporal	✓	Record Data Timestamps
Repeat	Loop	✓		RepeatCount
RepeatCount	Loop	✓		Repeat
ToArray	Collections	✓	Collect Input Data	ToList
ToList	Collections	✓		ToArray
ToDictionary	Collections	✓		ToLookup
ToLookup	Collections	✓		ToDictionary
AsyncSubject	Subject	✓		Other Subjects
BehaviorSubject	Subject	✓		Other Subjects
PublishSubject	Subject	✓		Other Subjects
ReplaySubject	Subject	✓		Other Subjects
BufferCount	Group	✓		BufferTime WindowCount
BufferTime	Group	✓		BufferCount WindowTime
WindowCount	Group	✓		WindowTime BufferCount
WindowTime	Group	✓		WindowCount BufferTime
BufferTrigger	Dynamic Group	✓		WindowTrigger
WindowTrigger	Dynamic Group	✓		BufferTrigger Window
Window	Dynamic Group	✓		WindowTrigger
Amb	Dynamic Switch	✓		Switch
Switch	Dynamic Switch	✓		Amb
Dematerialize	Logging	✓
ElementIndex	Logging	✓
IgnoreElements	Logging	✓
IsEmpty	Logging	✓
Materialize	Logging	✓
Retry	Exception	✓		RetryCount
RetryCount	Exception	✓		Retry
Timeout	Exception	✓
Catch	Dynamic Exception	✓		Retry OnErrorResumeNext
OnErrorResumeNext	Dynamic Exception	✓		Concat Catch
SequenceEqual	Dynamic Exception	✓
Prepend	Element Insertion	✓		Append
Append	Element Insertion	✓		Prepend
DistinctBy	Key Filtering	*
DistinctUntilChangedBy	Key Filtering	*
GroupBy	Key Filtering	*
MaxBy	Key Filtering	*
MinBy	Key Filtering	*
OrderBy	Key Sorting	*
OrderByDescending	Key Sorting	*
ThenBy	Key Sorting	*
ThenByDescending	Key Sorting	*
CreateObservable	Higher-Order	✓		SelectMany
SelectMany	Higher-Order	✓		CreateObservable
Visualizer	Sinks	✓
Sink	Sinks	✓

Comments (*)

• For Throttle, it was hard to build a basic example using just Bonsai.Core reactive operators, since it relies on an input with a variable rate, so I used KeyDown as an input.
• CreateTimestamped was renamed from CombineTimestamp, but the accompanying doc files were not updated yet; these files were renamed. In addition, the existing example (to carry forward the timestamp) was adopted as a basic example. While it is more like an application example, I could not figure out how to generate a basic example without copying much of that workflow. In addition, a true basic example for this operator would rely on timestamps coming from a different source.
• For the key filtering and sorting operators (like GroupBy, OrderBy), the basic examples are a little complicated because of the steps needed to set up the key/value collection. I grouped the Key and Value manipulations to somewhat hide them, as I think they're not essential for understanding how the operators work, but I am open to other suggestions on how to simplify them.

Operators without examples

Operator	Category	Comment
ResourceSubject	Subject	- Used for niche applications involving device operators? - Unsure how to create a basic or suitable application example. - I listed AsyncSubject as an alternative due to prior confusion.
ObserveOn SubscribeOn	Scheduler	- Unsure about how to create examples for them. - Would Timer -> SubscribeOn (DefaultScheduler) -> ObserveOn (NewThreadScheduler) -> Accumulate work?
CurrentThreadScheduler DefaultScheduler EventLoopScheduler ImmediateScheduler NewThreadScheduler TaskPoolScheduler ThreadPoolScheduler	Scheduler Objects	- Unsure how to use them. - Unsure as to when someone would use them given that they also appear as property options for ObserveOn and SubscribeOn.
Synchronize	Exception	- Very niche operator used to patch custom implementations
Publish Replay	Nested Subjects	- Not sure how to use them in place of their regular subject variant. - Can be used to unlock more complex functionality?
Defer	Higher-Order	- Not sure how to illustrate its behaviour with muliple subscribers I mainly use it as my default closed-scope node

Other Thoughts/Issues

• Haven't decided whether to add higher-order examples for operators that have a higher-order counterpart (like Concat)
• In many cases, I think the description for the basic example closely mirrors the editor description for the operator, so I might just take those out and leave only descriptions for the application examples. I will probably leave it for one of the last edits so it can be reversed if necessary.
• The section that follows with the class declaration code snippet, inheritance, and inherited members does not have a section heading. That makes it appear as a continuation of the examples or alternatives. I think adding a section heading is needed, but I will also probably add it as an edit near the end.
• For collection operators (ToList, etc), I thought it would be helpful to add some references to .NET documentation for the collection, in case they need to be manipulated further. These were added to the existing summaries for each operator and do not affect the examples directly.
• In some of the more complicated examples, I used two VisualizerWindows to illustrate the elements before and after they have been processed by the operator, I have been wondering if that might be a good general strategy to apply to all the Reactive operators, even if it adds a bit of clutter.
• @glopesdev has also mentioned that we could consider listing the alternatives using the <seealso> tag for XML doc comments, there is an example of that in the existing documentation for the SubscribeOn operator.

[banchan86]

I updated this PR with the feedback from DCM and added another batch of reactive operators (operators that "combine" sequences). As such i changed the title of this PR and also added a chart in the top level comment to document which operators were included.

Other changes that were made:

• Switched basic types in basic examples to those from Bonsai.Core (Range/Int/Timer)
• Separated "basic examples" from "practical application examples"
  • One point we discussed was whether to even include practical/complex examples or leave them out. As I was covering the "combine" operators however, I discovered that there was already some mention of practical applications for the operators in the overwrite articles. Distinguishing between those operators was also hard with just basic examples. Thus, I opted to include practical examples/applications for them by simply expanding on those existing notes with workflow containers.
• Improved visualization of operators that only emit a final value by repeating the block
  • I noticed that the previous solution of using a delay node and a note to use ObjectTextVisualizer was very clunky and unintuitive.

[glopesdev]

Huge work, thanks for pushing this!

Took me a while to go through everything, and left a bunch of notes for myself to help me figure out how best to organize and try not to forget everything. In the middle I stopped repeating the same comment over and over.

Will now go again and probably try to put together a PR that addresses the comments directly to make it easier to work with.

[glopesdev]

Great work, thank you so much for this contribution, it's been a long time coming!