RxJava Cartestian Product

rxjava_cartesian_product.kt

import io.reactivex.Observable

fun main(args: Array<String>) {

    val sources = listOf(
        Observable.just(1, 2, 3, 4, 5),
        Observable.just(10, 20, 30, 40, 50),
        Observable.just(100, 200, 300, 400, 500)
    )
    var cartesianProduct: Observable<List<Int>>? = null
    for (obs in sources) {
        if (cartesianProduct == null) {
            cartesianProduct = obs.map { listOf(it) }
        } else {
            cartesianProduct = cartesianProduct.flatMap { list -> obs.map { list.plus(it) }}
        }
    }

    cartesianProduct!!.subscribe(::println)
}