Mastering Machine Learning with Spark 2.x

Directed and undirected graphs

In a pair of vertices that make up an edge e, by convention, we call the first vertex the source and the second one the target. The natural interpretation here is that the connection represented by edge e has a direction; it flows from the source to the target. Note that in Figure 1, the graph displayed is undirected; that is, we did not distinguish between the source and target.

Using the exact same definition, we can create a directed version of our graph, as shown in the following image. Note that the graph looks slightly different in the way it is presented, but the connections of vertices and edges remain unchanged:

Figure 2: A directed graph with the same topology as the previous one. In fact, forgetting ...