Streams, check that two lists of objects has same nested lists of another objects

Question

I have List of log events that I shoud check, that they are the same as should be. There is structure of Event object:

public class Event {
    public String type;
    public List<Item> items;

    public Event(String type, List<Item> items) {
        this.type = type;
        this.items = items;
    }
}
public class Item {
    public String id;
    public String value;

    public Item(String id, String value) {
        this.id = id;
        this.value = value;
    }
}

Lets fill "should" object, "real" object and check that they have same items

List<Event> should = asList(
                new Event("1000", asList(new Item("server_id", "1"), new Item("user_id", "11"))),
                new Event("1000", asList(new Item("server_id", "1"), new Item("user_id", "11"))));
        List<Event> logged = asList(
                new Event("1000", asList(new Item("server_id", "1"), new Item("user_id", "11"))),
                new Event("1000", asList(new Item("server_id", "1"), new Item("user_id", "11"))));
        boolean logMatch = logged.stream()
                                    .allMatch(e1 ->
                                            should.stream()
                                                      .allMatch(e2 -> e2.items
                                                                        .stream()
                                                                        .allMatch(a2 -> e1.items
                                                                                          .stream()
                                                                                          .anyMatch(a1 -> a1.value.equals(a2.value)))));
        System.out.println(logMatch);

It's true, but I have an issue, if I change any value of "should" to "11", I'll get true. How can I fix this or how to make this comparison simpler?

Are you checking that all `value` fields are equal on an item-to-item basis? — ernest_k, Oct 19 '18 at 09:21
@ernest_k i want to check that every Event from one list has same in another list. Events will be same if there id/value of all items will be the same. And i totally broke my brain when i tried to write this:) — callmedope, Oct 19 '18 at 09:25

ernest_k · Accepted Answer · 2018-10-19T10:21:21.247

3

Your problem is that you're just checking that each logged element has at least an element in the should list with which it has the same value. You rather want to check that the two value collections are equivalent.

A simple correction can use list comparison in this case:

List<String> actualValues =  logged.stream().flatMap(l -> l.items.stream())
        .map(i -> i.value).collect(Collectors.toList());
List<String> shouldValues = should.stream().flatMap(l -> l.items.stream())
        .map(i -> i.value).collect(Collectors.toList());

boolean logMatch = actualValues.equals(shouldValues);

This comparison is strict and takes order into account. If you'd rather ignore the order of elements, you can collect to set to ignore the order of items.

EDIT: You can compare actual events if you need to check multiple fields. The following uses a predicate:

List<Item> actualValues =  logged.stream().flatMap(l -> l.items.stream())
        .collect(Collectors.toList());
List<Item> shouldValues = should.stream().flatMap(l -> l.items.stream())
        .collect(Collectors.toList());

BiPredicate<Item, Item> predicate = (item1, item2) -> item1.id.equals(item2.id) 
        && item1.value.equals(item2.value);

boolean res = actualValues.size() == shouldValues.size() //should be same length
        && IntStream.range(0, actualValues.size())
        .filter(i -> !predicate.test(actualValues.get(i), shouldValues.get(i)))
        .count() == 0; //all elements's ID and value must match

edited Oct 19 '18 at 10:21

answered Oct 19 '18 at 09:29

ernest_k

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Thnx! what about if I want to check both id and value? Check pls UPD of question, i posted – callmedope Oct 19 '18 at 09:45
nice :) but you've made mistake here -> !predicate.test(actualValues.get(i), actualValues.get(i)) – callmedope Oct 19 '18 at 10:19
hi! Can you give me an advice? What if i want to check Events in any order? I found that same event can be pushed to logger with delay :) – callmedope Oct 23 '18 at 10:52
@callmedope I mentioned that in the original post. Just change to `....collect(Collectors.toSet());` and redeclare those variables as `Set`. Sets would not take order into account. – ernest_k Oct 23 '18 at 10:58
thnx, i will try :) – callmedope Oct 23 '18 at 12:27
wait, but if i want to compare 2 values, i cant collect them to Set – callmedope Oct 23 '18 at 13:39
@callmedope can you elaborate? – ernest_k Oct 23 '18 at 14:10
@ernetst_k https://stackoverflow.com/questions/53536678/how-to-compare-list-of-objects-with-nested-lists :) – callmedope Nov 29 '18 at 12:17

Streams, check that two lists of objects has same nested lists of another objects

1 Answers1