site/source/docs/datafu/guide/link-analysis.html.markdown.erb

---
title: Link Analysis - Guide - Apache DataFu Pig
version: 1.6.0
section_name: Apache DataFu Pig - Guide
license: >
   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
---

## Link Analysis

### PageRank

Run PageRank on a large number of independent graphs through the [PageRank UDF](https://datafu.apache.org/docs/datafu/<%= current_page.data.version %>/datafu/pig/linkanalysis/PageRank.html):

```pig
define PageRank datafu.pig.linkanalysis.PageRank('dangling_nodes','true');

topic_edges = LOAD 'input_edges' as (topic:INT,source:INT,dest:INT,weight:DOUBLE);

topic_edges_grouped = GROUP topic_edges by (topic, source) ;
topic_edges_grouped = FOREACH topic_edges_grouped GENERATE
  group.topic as topic,
  group.source as source,
  topic_edges.(dest,weight) as edges;

topic_edges_grouped_by_topic = GROUP topic_edges_grouped BY topic;

topic_ranks = FOREACH topic_edges_grouped_by_topic GENERATE
  group as topic,
  FLATTEN(PageRank(topic_edges_grouped.(source,edges))) as (source,pr);

skill_ranks = FOREACH skill_ranks GENERATE
  topic, source, pr;
```

This implementation stores the nodes and edges (mostly) in memory. It is therefore best suited when one needs to compute PageRank on many reasonably sized graphs in parallel.