Unary Graph Collection Operators

This section provides an overview of unary graph collection operators, which operate on a single GraphCollection and return a subset or transformation of the input collection.

Unary Graph Collection Operators
Selection
Matching
Limit
Distinct

Selection

Given a collection, the select operator filters all contained graphs based on their associated graph head and return a collection with logical graphs that fulfill the predicate.

Method	Expects	Returns
select	predicate function (`FilterFunction<GraphHead>`) for a graph head	`GraphCollection` which contains all logical graphs that fulfill the predicate.

Selection example

Consider the Social Network example graph, which contains multiple logical graphs with different relations. This example takes a single graph collection and selects a subset of logical graphs that fulfill the predicate function.
In order to select all graphs that contain edges labeled 'hasMember', we would do the following:

FlinkAsciiGraphLoader loader = getSocialNetworkLoader();

GraphCollection collection = loader.getGraphCollectionByVariables("g0", "g1", "g2", "g3");

// In order to select graphs that contain a certain edge label (in this case, 'hasMember'),
// we need to aggregate a property 'hasEdgeLabel_<label>' to determine if a give label is present or not.
// Since aggregated properties are added to the graph head, it is then possible
// to use the select method to retrieve graphs which are of interest to us.
HasEdgeLabel hasLabelHasMember = new HasEdgeLabel("hasMember"):

// apply aggregation
collection = collection.apply(new ApplyAggregation(hasLabelHasMember))

// select graphs
GraphCollection result = collection.select(hasLabelHasMember))

The graph collection result now contains the logical graph g3:Forum, since it is the only one which contains edges labeled 'hasMember'. Or to be more precise: it is the only one with a property 'hasEdgeLabel_hasMember' that is set to true after we applied the aggregation.