[jira] [Comment Edited] (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=14976525#comment-14976525 ] 

Martin Junghanns edited comment on FLINK-2905 at 10/27/15 3:05 PM:
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Sorry for the confusion. In the example, I focused on the graphs that are induced by the vertex intersection (1 and 3 in that case). You are right, in call 1, resulting edges are the union of all input edges with identical source, target and edge values. I think, computing distinct edges would be too strict for some cases. Consider a real world example where you want to intersect two transportation networks between cities, one for trains and one for planes. Each edge has a maximum transportation capacity. There can be a case, where you have two identical edge values in both networks between the same cities. If we compute distinct, it is not possible to aggregate edges by their value (to get the total capacity). Keeping edges from both graphs allows us to compute such aggregates. If the user is not interested in duplicates, a distinct call is always possible and does not invalidate the graph.


was (Author: mju):
Sorry for the confusion. In the example, I focused on the graphs that are induced by the vertex intersection (1 and 3 in that case). You are right, in call 1, resulting edges are the union of all input edges with identical source target and edge values. I think, computing distinct edges would be too strict for some cases. Consider a real world example where you want to intersect two transportation networks between cities, one for trains and one for planes. Each edge has a maximum transportation capacity. There can be a case, where you have two identical edge values in both networks between the same cities. If we compute distinct, it is not possible to aggregate edges by their value (to get the total capacity). Keeping edges from both graphs allows us to compute such aggregates. If the user is not interested in duplicates, a distinct call is always possible and does not invalidate the graph.

> 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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