commons-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Mark Shead (JIRA)" <>
Subject [jira] Created: (COLLECTIONS-359) A ∩ B != B ∩ A when duplicates are present in a list
Date Mon, 05 Jul 2010 15:01:52 GMT
A  ∩ B  !=  B  ∩ A when duplicates are present in a list

                 Key: COLLECTIONS-359
             Project: Commons Collections
          Issue Type: Bug
          Components: Collection
    Affects Versions: 3.2
            Reporter: Mark Shead

When duplicates are present in a list, ListUtils.intersection doesn't behave as expected.
The intersection of two lists should give the same result regardless of which list comes first.
ListUtils.intersection(A,B) should equal ListUtils.intersection(B,A).  This is not the case
when the list contains duplicates.

Right now:
 [a, b]  ∩  [a, a, b, b] =  [a, a, b, b]
 [a, a, b, b]  ∩  [a, b] =  [a, b]

Expected behavior:

 [a, a, b, b]  ∩  [a, b] =  [a, b]
 [a, b]  ∩  [a, a, b, b] =  [a, b]

Code demonstrating the problem.

		List A = new ArrayList();
		List B = new ArrayList();
		System.out.println("List A: " + A);
		System.out.println("List B: " + B);
		System.out.println("A ∩ B = " + ListUtils.intersection(A,B));
		System.out.println("B ∩ A = " +ListUtils.intersection(B,A));


List A: [a, b]
List B: [a, a, b, b]
A ∩ B = [a, a, b, b]
B ∩ A = [a, b]

This message is automatically generated by JIRA.
You can reply to this email to add a comment to the issue online.

View raw message