I'm open to use a lib. I just want something simple to diff two collections on a different criteria than the normal equals function.
Right now I use something like :
collection1.stream()
.filter(element -> !collection2.stream()
.anyMatch(element2 -> element2.equalsWithoutSomeField(element)))
.collect(Collectors.toSet());
and I would like something like :
Collections.diff(collection1, collection2, Foo::equalsWithoutSomeField);
(edit) More context:
Should of mentioned that I'm looking for something that exists already and not to code it myself. I might code a small utils from your ideas if nothing exists.
Also, Real duplicates aren't possible in my case: the collections are Sets. However, duplicates according to the custom equals are possible and should not be removed by this operation. It seems to be a limitation in a lot of possible solutions.
You can use UnifiedSetWithHashingStrategy
from Eclipse Collections. UnifiedSetWithHashingStrategy
allows you to create a Set with a custom HashingStrategy
.
HashingStrategy
allows the user to use a custom hashCode()
and equals()
. The Object's hashCode()
and equals()
is not used.
Edit based on requirement from OP via comment:
You can use reject()
or removeIf()
depending on your requirement.
Code Example:
// Common code
Person person1 = new Person("A", "A");
Person person2 = new Person("B", "B");
Person person3 = new Person("C", "A");
Person person4 = new Person("A", "D");
Person person5 = new Person("E", "E");
MutableSet<Person> personSet1 = Sets.mutable.with(person1, person2, person3);
MutableSet<Person> personSet2 = Sets.mutable.with(person2, person4, person5);
HashingStrategy<Person> hashingStrategy =
HashingStrategies.fromFunction(Person::getLastName);
1) Using reject()
: Creates a new Set
which contains all the elements which do not satisfy the Predicate
.
@Test
public void reject()
{
MutableSet<Person> personHashingStrategySet = HashingStrategySets.mutable.withAll(
hashingStrategy, personSet2);
// reject creates a new copy
MutableSet<Person> rejectSet = personSet1.reject(personHashingStrategySet::contains);
Assert.assertEquals(Sets.mutable.with(person1, person3), rejectSet);
}
2) Using removeIf()
: Mutates the original Set
by removing the elements which satisfy the Predicate
.
@Test
public void removeIfTest()
{
MutableSet<Person> personHashingStrategySet = HashingStrategySets.mutable.withAll(
hashingStrategy, personSet2);
// removeIf mutates the personSet1
personSet1.removeIf(personHashingStrategySet::contains);
Assert.assertEquals(Sets.mutable.with(person1, person3), personSet1);
}
Answer before requirement from OP via comment: Kept for reference if others might find it useful.
3) Using Sets.differenceInto()
API available in Eclipse Collections:
In the code below, set1
and set2
are the two sets which use Person
's equals()
and hashCode()
. The differenceSet
is a UnifiedSetWithHashingStrategy
so, it uses the lastNameHashingStrategy
to define uniqueness. Hence, even though set2
does not contain person3
however it has the same lastName as person1
the differenceSet
contains only person1
.
@Test
public void differenceTest()
{
MutableSet<Person> differenceSet = Sets.differenceInto(
HashingStrategySets.mutable.with(hashingStrategy),
set1,
set2);
Assert.assertEquals(Sets.mutable.with(person1), differenceSet);
}
Person class common to both code blocks:
public class Person
{
private final String firstName;
private final String lastName;
public Person(String firstName, String lastName)
{
this.firstName = firstName;
this.lastName = lastName;
}
public String getFirstName()
{
return firstName;
}
public String getLastName()
{
return lastName;
}
@Override
public boolean equals(Object o)
{
if (this == o)
{
return true;
}
if (o == null || getClass() != o.getClass())
{
return false;
}
Person person = (Person) o;
return Objects.equals(firstName, person.firstName) &&
Objects.equals(lastName, person.lastName);
}
@Override
public int hashCode()
{
return Objects.hash(firstName, lastName);
}
}
Javadocs: MutableSet, UnifiedSet, UnifiedSetWithHashingStrategy, HashingStrategy, Sets, reject, removeIf
Note: I am a committer on Eclipse Collections