Implement countByEach on RichIterable.

[donraab]

This can be implemented as a default method on RichIterable as countBy was. It will need appropriate co-variant overrides as default methods and optimizations for Bag implementations.

The signature of countByEach should be:

default <V> Bag<V> countByEach(Function<? super T, ? extends Iterable<V>> function)

The naming is based on the pattern we used for groupBy/groupByEach.

This code in the Pet Kata can then be improved.

Before:

MutableList<Person> people = ...;
MutableList<PetType> petTypes = people.flatCollect(Person::getPetTypes);
Bag<PetType> petTypeCounts = petTypes.toBag();
int cats = petTypeCounts.occurrencesOf(PetType.CAT);

After:

MutableList<Person> people = ...;
Bag<PetType> petTypeCounts = people.countByEach(Person::getPetTypes);
int cats = petTypeCounts.occurrencesOf(PetType.CAT);

http://eclipse.github.io/eclipse-collections-kata/pet-kata/#/6/2

[TheLoneKing]

Should the implementation be lazy?

[nikhilnanivadekar]

Yes similar to countBy()
countBy(): this.asLazy().<V>collect(function).toBag();

countByEach(): this.asLazy().<V>flatCollect(function).toBag();

[TheLoneKing]

the test case for this is failing with the error No iteration patterns should delegate to iterator().

Failed tests:
UnifiedMapNoIteratorTest.RichIterable_countByEach No iteration patterns should delegate to iterator()
UnifiedMapWithHashingStrategyNoIteratorTest.RichIterable_countByEach No iteration patterns should delegate to iterator()

My test case is here: https://github.com/TheLoneKing/eclipse-collections/blob/0dd3ca235272c9f9dc023ab9f90afee69c892b69/unit-tests-java8/src/test/java/org/eclipse/collections/test/RichIterableTestCase.java#L1626

Can someone please help me with the cause of this error?

[nikhilnanivadekar]

@TheLoneKing you are missing overrides for the countByEach() implementation. Take a look at countBy() for the overrides that are present.
I have simplified the test case and fixed it for Map here: nikhilnanivadekar@6f9ea99
Take a look and let me know if you have any questions.

Eclipse Collections Maps and Sets are backed by flattened arrays so iterating over them using an iterator() is inefficient.

[joshuacheng]

Working on this at UIUC HackNight.

[joshuakim0724]

I'll help you work on this @joshuacheng

[brianwang1217]

me too @joshuacheng @joshuakim0724