Bidirectional Multimap

[Francis Giraldeau]

I needed a Multimap that was also keeping reverse entry relationship, a kind of non-bijective bidirectional map where duplicated values are not allowed. AFAIK, there is not such collection in Guava, so I did a QND prototype:

https://github.com/giraldeau/lttng-studio/blob/master/org.lttng.studio.bundle/src/org/lttng/studio/collect/ArrayListBiMultimap.java

https://github.com/giraldeau/lttng-studio/blob/master/org.lttng.studio.tests/src/org/lttng/studio/collect/TestArrayListBiMultimap.java

Unfortunately, BiMap and Multimap can't be implemented at the same time, because get() return value type is conflicting.

Usage example: 

  ArrayListBiMultimap<String, String> m = test.new ArrayListBiMultimap<String, String>();

  m.put("foo", "bar");

  m.put("foo", "baz");

  forward map:

  {foo=[bar, baz]}

  reverse map:

  {baz=foo, bar=foo}

Could it be interesting for Guava? 

Cheers, 

Francis

[Louis Wasserman]

We have a BiMultimap internally, but haven't open-sourced it due to lack of demand -- though we do have ImmutableMultimap.inverse(), which helps users who are satisfied with immutability.  

Could you describe your use case in more detail?

(Additionally, ImmutableMultimap.inverse() has

Francis

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Louis Wasserman

[Louis Wasserman]

Also relevant: Guava issue 394.

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Louis Wasserman

[Francis Giraldeau]

Here is more info on the use case. I do have a graph composed of vertices. Vertices belong to some owner object. it must be quick to lookup the owner of a vertex, or to get the list of vertex for some owner. The relation between Owner and Vertex is one to many. Holding a reference to the owner inside the vertex is inelegant, because it creates a dependency between a Vertex, that is pure graph class and domain dependent owner class.

Bidirectional map for many-to-many relationship is probably the most general case, thought.

Cheers, 

Francis

[Louis Wasserman]

Is the graph mutable, or immutable?

If immutable, this would probably be satisfied with ImmutableMap.asMultimap(), which will be in release 14:

ImmutableMap<Vertex, Owner> ownerMap;

ImmutableMultimap<Owner, Vertex> vertexMultimap = ownerMap.asMultimap().inverse();

Louis Wasserman
wasserm...@gmail.com
http://profiles.google.com/wasserman.louis

[Gregory Kick]

Also, if you really want a representation of a graph, I've heard that http://jung.sourceforge.net/ is good.

Greg Kick
Java Core Libraries Team

[Grzegorz Rożniecki]

About Jung, there's Jung 3 beta version hosted on Google Code (http://code.google.com/p/jung/) which uses Guava instead of Apache Commons-Collections generics port (see migration guide), but seems to be inactive for some time now (but so does sourceforge version).

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Cheers,

Grzegorz Rożniecki

[Joshua O'Madadhain]

FWIW, JUNG is not precisely inactive, but the changes that we're working on haven't made it to the repositories yet.  

   Joshua O'Madadhain: Information Scientist, Musician, Philosopher-At-Tall
  "It's that moment of dawning comprehension that I live for" -- Bill Watterson

[Grzegorz Rożniecki]

That's great to hear because we use Jung 2 in our project and it's the only part depending on Apache Collections so I'd like to see Guava port. 

Out of curiosity, when is Jung 3 expected to come out?

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Cheers,

Grzegorz Rożniecki

[Joshua O'Madadhain]

On Sat, Nov 10, 2012 at 5:15 AM, Grzegorz Rożniecki <xaer...@gmail.com> wrote:

That's great to hear because we use Jung 2 in our project and it's the only part depending on Apache Collections so I'd like to see Guava port. 

Out of curiosity, when is Jung 3 expected to come out?

That is under discussion at the moment, but not until early 2013.  There are a couple of options we're considering.