List of Lists GroupBy-CodePudding

How can I succesfully do something like this?

trips.groupBy { Passenger::name if Passenger in it.passengers}

I want to reorder the List<Trips> which has a List<Passengers> to be [PassengerA: List<Trips>, PassengerB:...]

CodePudding user response：

If I understood your question correctly, this could be a way to do what you want:

val passengersToTrips = trips
    .flatMap { trip ->
        // Associate every passenger in a trip to the trip: this results in a List<Pair<Passenger, Trip>>
        trip.passengers.map { passenger -> passenger to trip }
    }
    .groupBy(
        // Group using the passenger as key (use passenger.name in case the name should be the key)
        keySelector = { (passenger, _) -> passenger },
        // Extracting only the trip from the pair to transform from List<Pair<Passenger, Trip> into List<Trip> 
        valueTransform = { (_, trip) -> trip }
    )