GS Collections Kata w/ JCF Solutions

[Raab, Donald]

Great suggestion.  I just gave it a try.  Max takes a comparator and returns Optional so you have to add a call to get().  I was able to change the example to the following:

Map<Double, Collection<Customer>> multimap = this.company.getCustomers()
    .stream()
    .collect(Collectors.<Customer, Double>groupBy((Customer customer) ->
        customer.getOrders()
            .stream()
            .explode((Stream.Downstream<LineItem> downstream, Order order) -> {
                downstream.send(order.getLineItems());
            })
            .map(LineItem::getValue)
            .max(Comparators.naturalOrder())
            .get()));

I get an unchecked error on Comparators.naturalOrder() in IntelliJ, but adding <Double> there makes it ugly.

This is the GS Collections version of the kata, which also used max(), but calls this method on a DoubleIterable:

MutableListMultimap<Double, Customer> multimap = this.company.getCustomers()
    .groupBy(customer -> customer.getOrders()
        .asLazy()
        .flatCollect(Order::getLineItems)
        .collectDouble(LineItem::getValue)
        .max());

Unfortunately, the type inference seems to be very successful at thwarting me trying to simplify the above example using the stream library features.  I would like to simplify down to this but can't seem to get it to work:

Map<Double, Collection<Customer>> multimap = this.company.getCustomers()
    .stream()
    .collect(groupBy((customer) ->
        customer.getOrders()
            .stream()
            .explode((downstream, order) -> {
                downstream.send(order.getLineItems());
            })
            .map(LineItem::getValue)
            .max(Comparators.naturalOrder())
            .get()));


From: Joe Bowbeer [mailto:joe.bowbeer at gmail.com] 
Sent: Wednesday, January 16, 2013 4:21 PM
To: Raab, Donald [Tech]
Cc: lambda-libs-spec-experts at openjdk.java.net; Motlin, Craig P. [Tech]; Weir, John [Tech]
Subject: Re: GS Collections Kata w/ JCF Solutions

Thanks.


Would it be better to rewrite the following using Stream.max()?


.reduce(0.0, (x, y) -> Math.max(x, y))

--Joe