[jira] Created: (COLLECTIONS-359) A ∩ B != B ∩ A when duplicates are present in a list

classic Classic list List threaded Threaded
3 messages Options
Reply | Threaded
Open this post in threaded view
|

[jira] Created: (COLLECTIONS-359) A ∩ B != B ∩ A when duplicates are present in a list

ASF GitHub Bot (Jira)
A  ∩ B  !=  B  ∩ A when duplicates are present in a list
--------------------------------------------------------

                 Key: COLLECTIONS-359
                 URL: https://issues.apache.org/jira/browse/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]
and
 [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();
                A.add("a");
                A.add("b");
                B.add("a");
                B.add("a");
                B.add("b");
                B.add("b");
                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));

output:

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.

Reply | Threaded
Open this post in threaded view
|

[jira] Updated: (COLLECTIONS-359) A ∩ B != B ∩ A when duplicates are present in a list

ASF GitHub Bot (Jira)

     [ https://issues.apache.org/jira/browse/COLLECTIONS-359?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Mark Shead updated COLLECTIONS-359:
-----------------------------------

    Attachment: COLLECTIONS-359.patch

This patch fixes the problem and adds a unit test that will fail when the problem remains.

> A  ∩ B  !=  B  ∩ A when duplicates are present in a list
> --------------------------------------------------------
>
>                 Key: COLLECTIONS-359
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-359
>             Project: Commons Collections
>          Issue Type: Bug
>          Components: Collection
>    Affects Versions: 3.2
>            Reporter: Mark Shead
>         Attachments: COLLECTIONS-359.patch
>
>
> 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]
> and
>  [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();
> A.add("a");
> A.add("b");
> B.add("a");
> B.add("a");
> B.add("b");
> B.add("b");
> 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));
> output:
> 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.

Reply | Threaded
Open this post in threaded view
|

[jira] Closed: (COLLECTIONS-359) A ∩ B != B ∩ A when duplicates are present in a list

ASF GitHub Bot (Jira)
In reply to this post by ASF GitHub Bot (Jira)

     [ https://issues.apache.org/jira/browse/COLLECTIONS-359?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Henri Yandell closed COLLECTIONS-359.
-------------------------------------

    Fix Version/s: 4.0-beta-1
       Resolution: Fixed

Thanks Mark. Patch applied.

svn ci -m "Applying Mark Shead's patch to COLLECTIONS-359. The intersection method was not handling duplicates correctly. "
Sending        src/java/org/apache/commons/collections/ListUtils.java
Sending        src/test/org/apache/commons/collections/TestListUtils.java
Transmitting file data ..
Committed revision 965173.


> A  ∩ B  !=  B  ∩ A when duplicates are present in a list
> --------------------------------------------------------
>
>                 Key: COLLECTIONS-359
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-359
>             Project: Commons Collections
>          Issue Type: Bug
>          Components: Collection
>    Affects Versions: 3.2
>            Reporter: Mark Shead
>             Fix For: 4.0-beta-1
>
>         Attachments: COLLECTIONS-359.patch
>
>
> 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]
> and
>  [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();
> A.add("a");
> A.add("b");
> B.add("a");
> B.add("a");
> B.add("b");
> B.add("b");
> 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));
> output:
> 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.