Returns an observable sequence containing a value that represents how many elements in the specified observable sequence satisfy a condition if provided, else the count of items.
Function): A function to test each element for a condition. The callback is called with the following information:
- the value of the element
- the index of the element
- the Observable object being subscribed
Any): Object to use as
Observable): An observable sequence containing a single element with a number that represents how many elements in the input sequence satisfy the condition in the predicate function if provided, else the count of items in the sequence.