GraphFrames：合并具有相似列值的边缘节点

问题描述

tl; dr：如何简化图，删除具有相同name值的边节点？

我有一个定义如下的图：

import graphframes
from pyspark.sql import SparkSession

spark = SparkSession.builder.getOrCreate()
vertices = spark.createDataFrame([
    ('1','foo','1'),('2','bar','2'),('3','3'),('4','5'),('5','baz','9'),('6','blah',('7',('8','3')
],['id','name','value'])

edges = spark.createDataFrame([
    ('1',('1','4'),'6'),'7'),'8')
],['src','dst'])

f = graphframes.GraphFrame(vertices,edges)

哪个会生成如下所示的图形（其中的数字表示顶点ID）：

从等于1的顶点ID开始，我想简化图形。这样，具有相似name值的节点将合并为一个节点。结果图看起来会有些变化 像这样：

请注意，我们如何只有一个foo（ID 1），一个bar（ID 2），一个baz（ID 5）和一个blah（ID 6 ）。顶点的value无关紧要，只是为了表明每个顶点都是唯一的。

我试图实现一个解决方案，但是它很hacky，效率极低，我敢肯定有更好的方法（我也不认为它可行）：

f = graphframes.GraphFrame(vertices,edges)

# Get the out degrees for our nodes. Nodes that do not appear in
# this dataframe have zero out degrees.
outs = f.outDegrees

# Merge this with our nodes.
vertices = f.vertices
vertices = f.vertices.join(outs,outs.id == vertices.id,'left').select(vertices.id,'value','outDegree')
vertices.show()

# Create a new graph with our out degree nodes.
f = graphframes.GraphFrame(vertices,edges)

# Find paths to all edge vertices from our vertex ID = 1
# Can we make this one operation instead of two??? What if we have more than two hops?
one_hop = f.find('(a)-[e]->(b)').filter('b.outDegree is null').filter('a.id == "1"')
one_hop.show()

two_hop = f.find('(a)-[e1]->(b); (b)-[e2]->(c)').filter('c.outDegree is null').filter('a.id == "1"')
two_hop.show()

# Super ugly,but union the vertices from the `one_hop` and `two_hop` above,and unique
# on the name.
vertices = one_hop.select('a.*').union(one_hop.select('b.*'))
vertices = vertices.union(two_hop.select('a.*').union(two_hop.select('b.*').union(two_hop.select('c.*'))))
vertices = vertices.dropDuplicates(['name'])
vertices.show()

# Do the same for the edges
edges = two_hop.select('e1.*').union(two_hop.select('e2.*')).union(one_hop.select('e.*')).distinct()

# We need to ensure that we have the respective nodes from our edges. We do this  by
# Ensuring the referenced vertex ID is in our `vertices` in both the `src` and the `dst`
# columns - This does NOT seem to work as I'd expect!
edges = edges.join(vertices,vertices.id == edges.src,"left").select("src","dst")
edges = edges.join(vertices,vertices.id == edges.dst,"dst")
edges.show()

是否有一种更简单的方法来删除节点（及其对应的边），以使边节点在其name上是唯一的？

解决方法

您为什么不简单地将name列视为新的id？

import graphframes

vertices = spark.createDataFrame([
    ('1','foo','1'),('2','bar','2'),('3','3'),('4','5'),('5','baz','9'),('6','blah',('7',('8','3')
],['id','name','value'])

edges = spark.createDataFrame([
    ('1',('1','4'),'6'),'7'),'8')
],['src','dst'])

#create a dataframe with only one column
new_vertices = vertices.select(vertices.name.alias('id')).distinct()

#replace the src ids with the name column
new_edges = edges.join(vertices,edges.src == vertices.id,'left')
new_edges = new_edges.select(new_edges.dst,new_edges.name.alias('src'))

#replace the dst ids with the name column
new_edges = new_edges.join(vertices,new_edges.dst == vertices.id,'left')
new_edges = new_edges.select(new_edges.src,new_edges.name.alias('dst'))

#drop duplicate edges
new_edges = new_edges.dropDuplicates(['src','dst'])

new_edges.show()
new_vertices.show()

f = graphframes.GraphFrame(new_vertices,new_edges)

输出：

+---+----+
|src| dst|
+---+----+
|foo| baz|
|foo| bar|
|baz|blah|
+---+----+

+----+
|  id|
+----+
|blah|
| bar|
| foo|
| baz|
+----+