thovex - 5 months ago 21

Scala Question

I have a graph of this form:

`_ 3 _`

/' '\

(1) (1)

/ \

1--(2)--->2

I want to count the most active user (who follow the most,here it's user 1 who follows two times user 2 and one time user 3).

My graph is of this form Graph[Int,Int]

`val edges = Array(Edge(1,10,1), Edge(10,1,1), Edge(11,1,1), Edge(1,11,1), Edge(1,12,1))`

val vertices = Array((12L,12), (10L,10), (11L,11), (1L,1))

val graph = Graph(sc.parallelize(vertices),sc.parallelize(edges),0)

My idea is to use to group srcId for the edges and to count using the iterator and then to sort but I have issues to use the iterator, the type are quite complex:

`graph.edges.groupBy(_.dstId).collect()`

Array[(org.apache.spark.graphx.VertexId,Iterable[org.apache.spark.graphx.Edge[Int]])]

Any ideas ?

Answer

Your idea of grouping by `srcId`

is good, since you are looking for the relation *follows* and not *is followed by* (your example uses `dstId`

by the way)

```
val group = graph.edges.groupBy(_.srcId)
```

*group* now contains the edges going out of each vertex. We can now take the sum of the attributes to get the total time the user follows any user.

```
val followCount = group.map{
case (vertex, edges) => (vertex, edges.map(_.attr).sum)
}.collect
```

Which produces

```
Array((10,1), (11,1), (1,3))
```

Now if you want to extract the user which follows the most, you can simply sort it by descending order and take the head of the list, which will give the most active user.

```
val mostActiveUser = followCount.sortBy(- _._2).head
```