Github user fobeligi commented on a diff in the pull request:
https://github.com/apache/flink/pull/2178#discussion_r68848469
--- Diff:
flink-libraries/flink-gelly/src/main/java/org/apache/flink/graph/Graph.java ---
@@ -408,6 +408,79 @@ public static GraphCsvReader fromCsvReader(String
edgesPath, ExecutionEnvironmen
}
/**
+ * Creates a graph from a Adjacency List text file with Vertex Key
values. Edges will be created automatically.
+ *
+ * @param filePath a path to an Adjacency List text file with the
Vertex data
+ * @param context the execution environment.
+ * @return An instance of {@link
org.apache.flink.graph.GraphAdjacencyListReader},
+ * on which calling methods to specify types of the Vertex ID, Vertex
value and Edge value returns a Graph.
+ */
+ public static GraphAdjacencyListReader fromAdjacencyListFile(String
filePath, ExecutionEnvironment context) {
+ return new GraphAdjacencyListReader(filePath, context);
+ }
+
+ /**
+ * Writes a graph as an Adjacency List formatted text file in a user
specified folder.
+ *
+ * @param filePath the path that the Adjacency List formatted text
file should be written in
+ * @param delimiters the delimiters that separate the different value
types in the Adjacency List formatted text
+ * file. Delimiters should be provided with the
following order:
+ * NEIGHBOR_DELIMITER : separating source from its
neighbors
+ * VERTICES_DELIMITER : separating the different
neighbors of a source vertex
+ * VERTEX_VALUE_DELIMITER: separating the source
vertex-id from the vertex value, as well as the
+ * target vertex-ids from the edge value.
+ */
+ public void writeAsAdjacencyList(String filePath, String... delimiters)
{
+
+ final String NEIGHBOR_DELIMITER = delimiters.length > 0 ?
delimiters[0] : "\t";
+
+ final String VERTICES_DELIMITER = delimiters.length > 1 ?
delimiters[1] : ",";
+
+ final String VERTEX_VALUE_DELIMITER = delimiters.length > 1 ?
delimiters[2] : "-";
+
+
+ DataSet<Tuple2<K, VV>> vertices = this.getVerticesAsTuple2();
+
+ DataSet<Tuple3<K, K, EV>> edgesNValues =
this.getEdgesAsTuple3();
--- End diff --
As I see now, we don't have to convert the vertex set to tuple2 set, so I
already changed that.
Regarding the edges dataset, in order to write the Adjacency List file, I
use the coGroup transformation to the Vertex dataset and EdgesAsTuple3 dataset,
where the vertexId equals the source of the edge.
In that case, even when a Vertex is source to no edges (e.g. has only
incoming edges), I can still have the vertexId in the "coGrouped" dataset (I
couldn't do that with a join).
I can't think how I could use the Edge dataset in a coGroup or similar
transformation.
Please let me know if you have any suggestions.
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