Select Many in Rx
.net, c#, system.reactive
Solution
`SelectMany` combines projection and flattening into a single step. Suppose you have a number of lists like `{ {1, 2}, {3, 4, 5}, { 6, 7 } }` you can use `SelectMany` to flatten it into a single list like: `{ 1, 2, 3, 4, 5, 6, 7}`
`SelectMany` in Rx can flatten multiple sequences into one observable (there are actually several overloads).
For a practical example, suppose you have a function `DownloadFile(filename)` which gives you an Observable which produces a value when the file completes downloading. You can now write:
string[] files = { "http://.../1", "http://.../2", "http://.../3" };
files.ToObservable()
.SelectMany(file => DownloadFile(file))
.Take(3)
.Subscribe(c => Console.WriteLine("Got " + c) , ()=> Console.WriteLine("Completed!"));
All 3 observables of `DownloadFile` are flattened into one, so you can wait for 3 values to arrive to see that all downloads are completed.
Problem
Please any one let me know how the `SelectMany` operator in Rx works. I don't know more about this operator in Linq either. Please explain this with the help of a simple example, and also in what occasion we will use this operator in Rx.