[jira] [Commented] (FLINK-2905) Add intersect method to Graph class

["Martin Junghanns (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-2905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14972499#comment-14972499 ] 

Martin Junghanns commented on FLINK-2905:
-----------------------------------------

Hi [~vkalavri]!

Short question: As we do not have unique identifiers on edges, I was wondering what the expected output according to the edges would be. Please consider the simple example:
V(G1):
{code}
1,1
2,2
3,3
4,4
5,5
{code}
V(G2)
{code}
1,1
3,3
6,6
{code}
E(G1)
{code}
1,2,12
1,3,13
1,3,14
{code}
E(G2)
{code}
1,3,13
1,6,26
6,3,63
{code}
Call
{code:java}
G' = G1.intersect(G2)
{code}
Expected output
V(G')
{code}
1,1
3,3
{code}
Option 1: Considering (source, target)
E(G')
{code}
1,3,13 // from G2
1,3,13 // from G1
1,3,14 // from G1
{code}
Option 2: Considering (source, target, value), no distinct
E(G')
{code}
1,3,13 // G1
1,3,13 // G2
{code}
Option 3: Considering (source, target, value), distinct
{code}
1,3,13 // G1 and G2
{code}
The underlying question is: What makes edges unique?

> Add intersect method to Graph class
> -----------------------------------
>
>                 Key: FLINK-2905
>                 URL: https://issues.apache.org/jira/browse/FLINK-2905
>             Project: Flink
>          Issue Type: New Feature
>          Components: Gelly
>    Affects Versions: 0.10
>            Reporter: Martin Junghanns
>            Assignee: Martin Junghanns
>            Priority: Minor
>
> Currently, the Gelly Graph supports the set operations {{Graph.union(otherGraph)}} and {{Graph.difference(otherGraph)}}. It would be nice to have a {{Graph.intersect(otherGraph)}} method, where the resulting graph contains all vertices and edges contained in both input graphs.



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