Java 8 - how to get multiple attributes of an object from a List?

Question

I have a list of locations returned by Google places API and decided to find a Place with a lowest price.

Here is how I implemented it with Java 8:

BigDecimal lowestPrice = places.stream()
                .collect(Collectors.groupingBy(Place::getPrice, Collectors.counting()))
                .entrySet().stream().min(Map.Entry.comparingByValue())
                .map(Map.Entry::getKey)
                .orElse(BigDecimal.ZERO);

It returns me the lowest price but it'll be great to get a name of the Place as well (it has a name attribute).

How can I also return a name of the place with a lowest price?

@GBlodgett I want to use the name an price values later so yes I need both. — samba
– samba, Commented Dec 9, 2018 at 21:37
Try places.stream().min(Comparator.comparing(Place::getPrice)).get(); — Hadi
– Hadi, Commented Dec 9, 2018 at 21:41
@HadiJ Right, cool since it's ambiguous what the OP is after I'll include both solutions then :). — Ousmane D.
– Ousmane D., Commented Dec 9, 2018 at 21:55

Wenneguen · Accepted Answer · 2018-12-09 21:44:20Z

9

Why don't you return the whole Place object ?

places.stream().min(Comparator.comparing(Place::getPrice)).get()

answered Dec 9, 2018 at 21:44

Wenneguen

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1 Comment

Donat Over a year ago

Good solution. You should rather return an Optional. .get() can make an exception if the list is empty.

Ousmane D. · Accepted Answer · 2018-12-09 22:07:29Z

Firstly, it's really unclear what you want as at first, you seem to say that

I have a list of locations returned by Google places API and decided to find a Place with a lowest price.

then at the bottom of your description, you say that:

It returns me the lowest price but it'll be great to get a name of the Place as well (it has a name attribute).

as if the latter seems to be what you want?

Nevertheless, here are both solutions:

if you want to find the min value by the count after grouping for whatever reason that may be... then you could do something along the lines of:

 places.stream()
       .collect(Collectors.groupingBy(Place::getPrice))
       .entrySet().stream()
       .min(Comparator.comparingInt((Map.Entry<Integer, List<Place>> e) -> e.getValue().size()))
       .map(e -> new SimpleEntry<>(e.getKey(), e.get(0)));

note that above i've used Integer as the entry key, feel free to change this to the appropriate type if it's not an Integer.

Otherwise, if you're simply after the object with the lowest price then you can do:

places.stream().min(Comparator.comparingInt(Place::getPrice));

or:

Collections.min(places, Comparator.comparingInt(Place::getPrice));

There's no need for grouping and all the stuff going on.

NoDataFound · Accepted Answer · 2018-12-09 21:49:45Z

You should find the Place with the lowest price, not the lowest price and Place that propose it:

places.stream()
      .min(Comparators.comparing(Place::getPrice)) // compare by Price. Should use a second criteria for Place with same Price
      ; // return Optional<Place>

If you really need to get the count, you can still do it:

  BigDecimal lowestPrice = places.stream()
            .collect(Collectors.groupingBy(Place::getPrice, toList()))
            .entrySet()
            .stream()
            .min(Map.Entry.comparingByKey()) // Optional<Map.Entry<BigDecimal, List<Place>>
            .map(Map.Entry::getValue)
            // places = List<Place>, you can use size()
            .ifPresent(places -> places.forEach(System.out::println));

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