events.cacheMap { x -> Result in
    // Closure executed once per unique `x`, replayed when not unique.
    expensiveOperation(x)
}

events.cacheMap(whenExceeding: .seconds(1)) { x -> Result in
    // Closure executed once per unique `x`, replayed when operation of unique value took 
    // longer than specified duration.
    expensiveOperation(x)
}

events.cacheFlatMapInvalidatingOn { x -> Observable<(Result, Date)> in
    // Closure executed once per unique `x`, replayed when input not unique. Cache 
    // invalidated when date returned is greater than or equal to date of event.
    expensiveOperation(x).map { output in 
        return (output, Date() + hours(1))
    }
}

// You can provide your own cache (disk, in-memory, etc.). NSCache is the default.
events.cacheMap(cache: MyCache()) { x -> Result in
    expensiveOperation(x)
}