implement Collection.unique()

blackdrag blackdrag added a comment - 25/Mar/05 3:24 PM Collection.unique sounds to me as you want to create a Set. Can you give a usecase where it is useful? What return value should the method have? List, Set, void? Is it modifying the list or not?

james strachan added a comment - 30/Mar/05 1:32 PM How about using coercion? set = [1, 2, 1, 2] as Set assert set instanceof Set assert set == [1, 2] Or maybe asSet() ?

Dierk Koenig added a comment - 08/Apr/05 5:30 AM for declaration: list = [1,1,1] as Set for use in path expressions: // returning a copy and changing the type list.toSet() // alternative list.asSet() // Set.toSet() should leave the Set untouched // or return a copy ? // modifying the receiver and returning it list.removeDupls()

Dierk Koenig added a comment - 07/Jul/05 4:06 AM unique() should not change the type of the Collection. the operation should be closed under its type.

Dierk Koenig added a comment - 07/Jul/05 9:28 AM /** Remove all duplicates from the Collection. Works on the receiver object and returns it. From any duplicate, the first that is returned by the Collections iterator is retained, all other instances are removed. The Collection's original sequence is retained. @param self @return self without duplicates */ public static Collection unique(Collection self){ if (self instanceof Set) return self; if (self.size() == new HashSet(self).size()) return self; Collection seen = new HashSet(self.size()); for (Iterator iter = self.iterator(); iter.hasNext() Unknown macro: { Object o = iter.next(); if (seen.contains(o)){ iter.remove(); } else { seen.add(o); } } return self; } Tests: class CollectionTest extends GroovyTestCase { void testUniqueOnListNoDupls() { assert [].unique() == [] assert [1].unique() == [1] assert [1,2].unique() == [1,2] def a = [1,2] assert a.is(a.unique()) } void testUniqueOnListOneDupl() { assert [1,1].unique() == [1] def a = [1,1] assert a.is(a.unique()) assert [1,2,1].unique() == [1,2] assert [1,2,1,1].unique() == [1,2] assert [1,1,2].unique() == [1,2] assert [1,1,2,1].unique() == [1,2] assert [1,1,2,1,1].unique() == [1,2] } void testUniqueOnListTwoDupls() { assert [1,1,2,2].unique() == [1,2] def a = [1,1,2,2] assert a.is(a.unique()) assert [1,2,1,2].unique() == [1,2] assert [1,2,1,1,2].unique() == [1,2] assert [1,1,2,2].unique() == [1,2] assert [1,1,2,1,2].unique() == [1,2] assert [1,1,2,2,1,1,2,2].unique() == [1,2] } void testUniqueOnOtherCollections() { def a = new HashSet([1,1]) assert a.is(a.unique()) assert 1 == a.size() a = new TreeSet([1,1]) assert a.is(a.unique()) assert 1 == a.size() a = new Vector([1,1]) assert a.is(a.unique()) assert 1 == a.size() a = new LinkedList([1,1]) assert a.is(a.unique()) assert 1 == a.size() } }