PageRank
Glossary
- Directed
-
Directed trait. The algorithm is well-defined on a directed graph.
- Directed
-
Directed trait. The algorithm ignores the direction of the graph.
- Directed
-
Directed trait. The algorithm does not run on a directed graph.
- Undirected
-
Undirected trait. The algorithm is well-defined on an undirected graph.
- Undirected
-
Undirected trait. The algorithm ignores the undirectedness of the graph.
- Heterogeneous nodes
-
Heterogeneous nodes fully supported. The algorithm has the ability to distinguish between nodes of different types.
- Heterogeneous nodes
-
Heterogeneous nodes allowed. The algorithm treats all selected nodes similarly regardless of their label.
- Heterogeneous relationships
-
Heterogeneous relationships fully supported. The algorithm has the ability to distinguish between relationships of different types.
- Heterogeneous relationships
-
Heterogeneous relationships allowed. The algorithm treats all selected relationships similarly regardless of their type.
- Weighted relationships
-
Weighted trait. The algorithm supports a relationship property to be used as weight, specified via the relationshipWeightProperty configuration parameter.
- Weighted relationships
-
Weighted trait. The algorithm treats each relationship as equally important, discarding the value of any relationship weight.
Introduction
The PageRank algorithm measures the importance of each node within the graph, based on the number incoming relationships and the importance of the corresponding source nodes. The underlying assumption roughly speaking is that a page is only as important as the pages that link to it.
PageRank is introduced in the original Google paper as a function that solves the following equation:
where,
-
we assume that a page A has pages T1 to Tn which point to it.
-
d is a damping factor which can be set between 0 (inclusive) and 1 (exclusive). It is usually set to 0.85.
-
C(A) is defined as the number of links going out of page A.
This equation is used to iteratively update a candidate solution and arrive at an approximate solution to the same equation.
For more information on this algorithm, see:
Running this algorithm requires sufficient memory availability. Before running this algorithm, we recommend that you read Memory Estimation. |
Considerations
There are some things to be aware of when using the PageRank algorithm:
-
If there are no relationships from within a group of pages to outside the group, then the group is considered a spider trap.
-
Rank sink can occur when a network of pages is forming an infinite cycle.
-
Dead-ends occur when pages have no outgoing relationship.
Changing the damping factor can help with all the considerations above. It can be interpreted as a probability of a web surfer to sometimes jump to a random page and therefore not getting stuck in sinks.
Syntax
This section covers the syntax used to execute the PageRank algorithm in each of its execution modes. We are describing the named graph variant of the syntax. To learn more about general syntax variants, see Syntax overview.
CALL gds.pageRank.stream(
graphName: String,
configuration: Map
)
YIELD
nodeId: Integer,
score: Float
Name | Type | Default | Optional | Description |
---|---|---|---|---|
graphName |
String |
|
no |
The name of a graph stored in the catalog. |
configuration |
Map |
|
yes |
Configuration for algorithm-specifics and/or graph filtering. |
Name | Type | Default | Optional | Description |
---|---|---|---|---|
List of String |
|
yes |
Filter the named graph using the given node labels. Nodes with any of the given labels will be included. |
|
List of String |
|
yes |
Filter the named graph using the given relationship types. Relationships with any of the given types will be included. |
|
Integer |
|
yes |
The number of concurrent threads used for running the algorithm. |
|
String |
|
yes |
An ID that can be provided to more easily track the algorithm’s progress. |
|
Boolean |
|
yes |
If disabled the progress percentage will not be logged. |
|
dampingFactor |
Float |
|
yes |
The damping factor of the Page Rank calculation. Must be in [0, 1). |
Integer |
|
yes |
The maximum number of iterations of Page Rank to run. |
|
Float |
|
yes |
Minimum change in scores between iterations. If all scores change less than the tolerance value the result is considered stable and the algorithm returns. |
|
String |
|
yes |
Name of the relationship property to use as weights. If unspecified, the algorithm runs unweighted. |
|
sourceNodes |
List of Node or Number |
|
yes |
The nodes or node ids to use for computing Personalized Page Rank. |
scaler |
String or Map |
|
yes |
The name of the scaler applied for the final scores. Supported values are |
Name | Type | Description |
---|---|---|
nodeId |
Integer |
Node ID. |
score |
Float |
PageRank score. |
CALL gds.pageRank.stats(
graphName: String,
configuration: Map
)
YIELD
ranIterations: Integer,
didConverge: Boolean,
preProcessingMillis: Integer,
computeMillis: Integer,
postProcessingMillis: Integer,
centralityDistribution: Map,
configuration: Map
Name | Type | Default | Optional | Description |
---|---|---|---|---|
graphName |
String |
|
no |
The name of a graph stored in the catalog. |
configuration |
Map |
|
yes |
Configuration for algorithm-specifics and/or graph filtering. |
Name | Type | Default | Optional | Description |
---|---|---|---|---|
List of String |
|
yes |
Filter the named graph using the given node labels. Nodes with any of the given labels will be included. |
|
List of String |
|
yes |
Filter the named graph using the given relationship types. Relationships with any of the given types will be included. |
|
Integer |
|
yes |
The number of concurrent threads used for running the algorithm. |
|
String |
|
yes |
An ID that can be provided to more easily track the algorithm’s progress. |
|
Boolean |
|
yes |
If disabled the progress percentage will not be logged. |
|
dampingFactor |
Float |
|
yes |
The damping factor of the Page Rank calculation. Must be in [0, 1). |
Integer |
|
yes |
The maximum number of iterations of Page Rank to run. |
|
Float |
|
yes |
Minimum change in scores between iterations. If all scores change less than the tolerance value the result is considered stable and the algorithm returns. |
|
String |
|
yes |
Name of the relationship property to use as weights. If unspecified, the algorithm runs unweighted. |
|
sourceNodes |
List of Node or Number |
|
yes |
The nodes or node ids to use for computing Personalized Page Rank. |
scaler |
String or Map |
|
yes |
The name of the scaler applied for the final scores. Supported values are |
Name | Type | Description |
---|---|---|
ranIterations |
Integer |
The number of iterations run. |
didConverge |
Boolean |
Indicates if the algorithm converged. |
preProcessingMillis |
Integer |
Milliseconds for preprocessing the graph. |
computeMillis |
Integer |
Milliseconds for running the algorithm. |
postProcessingMillis |
Integer |
Milliseconds for computing the |
centralityDistribution |
Map |
Map containing min, max, mean as well as p50, p75, p90, p95, p99 and p999 percentile values of centrality values. |
configuration |
Map |
The configuration used for running the algorithm. |
CALL gds.pageRank.mutate(
graphName: String,
configuration: Map
)
YIELD
nodePropertiesWritten: Integer,
ranIterations: Integer,
didConverge: Boolean,
preProcessingMillis: Integer,
computeMillis: Integer,
postProcessingMillis: Integer,
mutateMillis: Integer,
centralityDistribution: Map,
configuration: Map
Name | Type | Default | Optional | Description |
---|---|---|---|---|
graphName |
String |
|
no |
The name of a graph stored in the catalog. |
configuration |
Map |
|
yes |
Configuration for algorithm-specifics and/or graph filtering. |
Name | Type | Default | Optional | Description |
---|---|---|---|---|
mutateProperty |
String |
|
no |
The node property in the GDS graph to which the score is written. |
List of String |
|
yes |
Filter the named graph using the given node labels. |
|
List of String |
|
yes |
Filter the named graph using the given relationship types. |
|
Integer |
|
yes |
The number of concurrent threads used for running the algorithm. |
|
String |
|
yes |
An ID that can be provided to more easily track the algorithm’s progress. |
|
dampingFactor |
Float |
|
yes |
The damping factor of the Page Rank calculation. Must be in [0, 1). |
Integer |
|
yes |
The maximum number of iterations of Page Rank to run. |
|
Float |
|
yes |
Minimum change in scores between iterations. If all scores change less than the tolerance value the result is considered stable and the algorithm returns. |
|
String |
|
yes |
Name of the relationship property to use as weights. If unspecified, the algorithm runs unweighted. |
|
sourceNodes |
List of Node or Number |
|
yes |
The nodes or node ids to use for computing Personalized Page Rank. |
scaler |
String or Map |
|
yes |
The name of the scaler applied for the final scores. Supported values are |
Name | Type | Description |
---|---|---|
ranIterations |
Integer |
The number of iterations run. |
didConverge |
Boolean |
Indicates if the algorithm converged. |
preProcessingMillis |
Integer |
Milliseconds for preprocessing the graph. |
computeMillis |
Integer |
Milliseconds for running the algorithm. |
postProcessingMillis |
Integer |
Milliseconds for computing the |
mutateMillis |
Integer |
Milliseconds for adding properties to the projected graph. |
nodePropertiesWritten |
Integer |
The number of properties that were written to the projected graph. |
centralityDistribution |
Map |
Map containing min, max, mean as well as p50, p75, p90, p95, p99 and p999 percentile values of centrality values. |
configuration |
Map |
The configuration used for running the algorithm. |
CALL gds.pageRank.write(
graphName: String,
configuration: Map
)
YIELD
nodePropertiesWritten: Integer,
ranIterations: Integer,
didConverge: Boolean,
preProcessingMillis: Integer,
computeMillis: Integer,
postProcessingMillis: Integer,
writeMillis: Integer,
centralityDistribution: Map,
configuration: Map
Name | Type | Default | Optional | Description |
---|---|---|---|---|
graphName |
String |
|
no |
The name of a graph stored in the catalog. |
configuration |
Map |
|
yes |
Configuration for algorithm-specifics and/or graph filtering. |
Name | Type | Default | Optional | Description |
---|---|---|---|---|
List of String |
|
yes |
Filter the named graph using the given node labels. Nodes with any of the given labels will be included. |
|
List of String |
|
yes |
Filter the named graph using the given relationship types. Relationships with any of the given types will be included. |
|
Integer |
|
yes |
The number of concurrent threads used for running the algorithm. |
|
String |
|
yes |
An ID that can be provided to more easily track the algorithm’s progress. |
|
Boolean |
|
yes |
If disabled the progress percentage will not be logged. |
|
Integer |
|
yes |
The number of concurrent threads used for writing the result to Neo4j. |
|
String |
|
no |
The node property in the Neo4j database to which the score is written. |
|
dampingFactor |
Float |
|
yes |
The damping factor of the Page Rank calculation. Must be in [0, 1). |
Integer |
|
yes |
The maximum number of iterations of Page Rank to run. |
|
Float |
|
yes |
Minimum change in scores between iterations. If all scores change less than the tolerance value the result is considered stable and the algorithm returns. |
|
String |
|
yes |
Name of the relationship property to use as weights. If unspecified, the algorithm runs unweighted. |
|
sourceNodes |
List of Node or Number |
|
yes |
The nodes or node ids to use for computing Personalized Page Rank. |
scaler |
String or Map |
|
yes |
The name of the scaler applied for the final scores. Supported values are |
Name | Type | Description |
---|---|---|
ranIterations |
Integer |
The number of iterations run. |
didConverge |
Boolean |
Indicates if the algorithm converged. |
preProcessingMillis |
Integer |
Milliseconds for preprocessing the graph. |
computeMillis |
Integer |
Milliseconds for running the algorithm. |
postProcessingMillis |
Integer |
Milliseconds for computing the |
writeMillis |
Integer |
Milliseconds for writing result data back. |
nodePropertiesWritten |
Integer |
The number of properties that were written to Neo4j. |
centralityDistribution |
Map |
Map containing min, max, mean as well as p50, p75, p90, p95, p99 and p999 percentile values of centrality values. |
configuration |
Map |
The configuration used for running the algorithm. |
Examples
All the examples below should be run in an empty database. The examples use Cypher projections as the norm. Native projections will be deprecated in a future release. |
In this section we will show examples of running the PageRank algorithm on a concrete graph. The intention is to illustrate what the results look like and to provide a guide in how to make use of the algorithm in a real setting. We will do this on a small web network graph of a handful nodes connected in a particular pattern. The example graph looks like this:
CREATE
(home:Page {name:'Home'}),
(about:Page {name:'About'}),
(product:Page {name:'Product'}),
(links:Page {name:'Links'}),
(a:Page {name:'Site A'}),
(b:Page {name:'Site B'}),
(c:Page {name:'Site C'}),
(d:Page {name:'Site D'}),
(home)-[:LINKS {weight: 0.2}]->(about),
(home)-[:LINKS {weight: 0.2}]->(links),
(home)-[:LINKS {weight: 0.6}]->(product),
(about)-[:LINKS {weight: 1.0}]->(home),
(product)-[:LINKS {weight: 1.0}]->(home),
(a)-[:LINKS {weight: 1.0}]->(home),
(b)-[:LINKS {weight: 1.0}]->(home),
(c)-[:LINKS {weight: 1.0}]->(home),
(d)-[:LINKS {weight: 1.0}]->(home),
(links)-[:LINKS {weight: 0.8}]->(home),
(links)-[:LINKS {weight: 0.05}]->(a),
(links)-[:LINKS {weight: 0.05}]->(b),
(links)-[:LINKS {weight: 0.05}]->(c),
(links)-[:LINKS {weight: 0.05}]->(d);
This graph represents eight pages, linking to one another.
Each relationship has a property called weight
, which describes the importance of the relationship.
MATCH (source:Page)-[r:LINKS]->(target:Page)
RETURN gds.graph.project(
'myGraph',
source,
target,
{ relationshipProperties: r { .weight } }
)
Memory Estimation
First off, we will estimate the cost of running the algorithm using the estimate
procedure.
This can be done with any execution mode.
We will use the write
mode in this example.
Estimating the algorithm is useful to understand the memory impact that running the algorithm on your graph will have.
When you later actually run the algorithm in one of the execution modes the system will perform an estimation.
If the estimation shows that there is a very high probability of the execution going over its memory limitations, the execution is prohibited.
To read more about this, see Automatic estimation and execution blocking.
For more details on estimate
in general, see Memory Estimation.
CALL gds.pageRank.write.estimate('myGraph', {
writeProperty: 'pageRank',
maxIterations: 20,
dampingFactor: 0.85
})
YIELD nodeCount, relationshipCount, bytesMin, bytesMax, requiredMemory
nodeCount | relationshipCount | bytesMin | bytesMax | requiredMemory |
---|---|---|---|---|
8 |
14 |
696 |
696 |
"696 Bytes" |
Stream
In the stream
execution mode, the algorithm returns the score for each node.
This allows us to inspect the results directly or post-process them in Cypher without any side effects.
For example, we can order the results to find the nodes with the highest PageRank score.
For more details on the stream
mode in general, see Stream.
stream
mode:CALL gds.pageRank.stream('myGraph')
YIELD nodeId, score
RETURN gds.util.asNode(nodeId).name AS name, score
ORDER BY score DESC, name ASC
name | score |
---|---|
"Home" |
3.215681999884452 |
"About" |
1.0542700552146722 |
"Links" |
1.0542700552146722 |
"Product" |
1.0542700552146722 |
"Site A" |
0.3278578964488539 |
"Site B" |
0.3278578964488539 |
"Site C" |
0.3278578964488539 |
"Site D" |
0.3278578964488539 |
The above query is running the algorithm in stream
mode as unweighted
and the returned scores are not normalized.
Below, one can find an example for weighted graphs.
Another example shows the application of a scaler to normalize the final scores.
While we are using the stream mode to illustrate running the algorithm as weighted or unweighted , all the algorithm modes support this configuration parameter.
|
Stats
In the stats
execution mode, the algorithm returns a single row containing a summary of the algorithm result.
For example PageRank stats returns centrality histogram which can be used to monitor the distribution of PageRank score values across all computed nodes.
This execution mode does not have any side effects.
It can be useful for evaluating algorithm performance by inspecting the computeMillis
return item.
In the examples below we will omit returning the timings.
The full signature of the procedure can be found in the syntax section.
For more details on the stats
mode in general, see Stats.
CALL gds.pageRank.stats('myGraph', {
maxIterations: 20,
dampingFactor: 0.85
})
YIELD centralityDistribution
RETURN centralityDistribution.max AS max
max |
---|
3.2156829834 |
The centrality histogram can be useful for inspecting the computed scores or perform normalizations.
Mutate
The mutate
execution mode extends the stats
mode with an important side effect: updating the named graph with a new node property containing the score for that node.
The name of the new property is specified using the mandatory configuration parameter mutateProperty
.
The result is a single summary row, similar to stats
, but with some additional metrics.
The mutate
mode is especially useful when multiple algorithms are used in conjunction.
For more details on the mutate
mode in general, see Mutate.
mutate
mode:CALL gds.pageRank.mutate('myGraph', {
maxIterations: 20,
dampingFactor: 0.85,
mutateProperty: 'pagerank'
})
YIELD nodePropertiesWritten, ranIterations
nodePropertiesWritten | ranIterations |
---|---|
|
|
Write
The write
execution mode extends the stats
mode with an important side effect: writing the score for each node as a property to the Neo4j database.
The name of the new property is specified using the mandatory configuration parameter writeProperty
.
The result is a single summary row, similar to stats
, but with some additional metrics.
The write
mode enables directly persisting the results to the database.
For more details on the write
mode in general, see Write.
write
mode:CALL gds.pageRank.write('myGraph', {
maxIterations: 20,
dampingFactor: 0.85,
writeProperty: 'pagerank'
})
YIELD nodePropertiesWritten, ranIterations
nodePropertiesWritten | ranIterations |
---|---|
|
|
Weighted
By default, the algorithm is considering the relationships of the graph to be unweighted
, to change this behaviour we can use configuration parameter called relationshipWeightProperty
.
In the weighted
case, the previous score of a node send to its neighbors, is multiplied by the relationship weight and then divided by the sum of the weights of its outgoing relationships.
If the value of the relationship property is negative it will be ignored during computation.
Below is an example of running the algorithm using the relationship property.
stream
mode using relationship weights:CALL gds.pageRank.stream('myGraph', {
maxIterations: 20,
dampingFactor: 0.85,
relationshipWeightProperty: 'weight'
})
YIELD nodeId, score
RETURN gds.util.asNode(nodeId).name AS name, score
ORDER BY score DESC, name ASC
name | score |
---|---|
"Home" |
3.53751028396339 |
"Product" |
1.9357838291651097 |
"About" |
0.7452612763883698 |
"Links" |
0.7452612763883698 |
"Site A" |
0.18152677135466103 |
"Site B" |
0.18152677135466103 |
"Site C" |
0.18152677135466103 |
"Site D" |
0.18152677135466103 |
We are using stream mode to illustrate running the algorithm as weighted or unweighted , all the algorithm modes support this configuration parameter.
|
Tolerance
The tolerance
configuration parameter denotes the minimum change in scores between iterations.
If all scores change less than the configured tolerance
value the result stabilises, and the algorithm returns.
stream
mode using bigger tolerance
value:CALL gds.pageRank.stream('myGraph', {
maxIterations: 20,
dampingFactor: 0.85,
tolerance: 0.1
})
YIELD nodeId, score
RETURN gds.util.asNode(nodeId).name AS name, score
ORDER BY score DESC, name ASC
name | score |
---|---|
"Home" |
1.5812450669583336 |
"About" |
0.5980194356381945 |
"Links" |
0.5980194356381945 |
"Product" |
0.5980194356381945 |
"Site A" |
0.23374955154166668 |
"Site B" |
0.23374955154166668 |
"Site C" |
0.23374955154166668 |
"Site D" |
0.23374955154166668 |
In this example we are using tolerance: 0.1
, so the results are a bit different compared to the ones from stream example which is using the default value of tolerance
.
Note that the nodes 'About', 'Link' and 'Product' now have the same score, while with the default value of tolerance
the node 'Product' has higher score than the other two.
Damping Factor
The damping factor configuration parameter accepts values between 0 (inclusive) and 1 (exclusive). If its value is too high then problems of sinks and spider traps may occur, and the values may oscillate so that the algorithm does not converge. If it’s too low then all scores are pushed towards 1, and the result will not sufficiently reflect the structure of the graph.
stream
mode using smaller dampingFactor
value:CALL gds.pageRank.stream('myGraph', {
maxIterations: 20,
dampingFactor: 0.05
})
YIELD nodeId, score
RETURN gds.util.asNode(nodeId).name AS name, score
ORDER BY score DESC, name ASC
name | score |
---|---|
"Home" |
1.2487309425844906 |
"About" |
0.9708121818724536 |
"Links" |
0.9708121818724536 |
"Product" |
0.9708121818724536 |
"Site A" |
0.9597081216238426 |
"Site B" |
0.9597081216238426 |
"Site C" |
0.9597081216238426 |
"Site D" |
0.9597081216238426 |
Compared to the results from the stream example which is using the default value of dampingFactor
the score values are closer to each other when using dampingFactor: 0.05
.
Also, note that the nodes 'About', 'Link' and 'Product' now have the same score, while with the default value of dampingFactor
the node 'Product' has higher score than the other two.
Personalised PageRank
Personalized PageRank is a variation of PageRank which is biased towards a set of sourceNodes
.
This variant of PageRank is often used as part of recommender systems.
The following examples show how to run PageRank centered around 'Site A'.
MATCH (siteA:Page {name: 'Site A'})
CALL gds.pageRank.stream('myGraph', {
maxIterations: 20,
dampingFactor: 0.85,
sourceNodes: [siteA]
})
YIELD nodeId, score
RETURN gds.util.asNode(nodeId).name AS name, score
ORDER BY score DESC, name ASC
name | score |
---|---|
"Home" |
0.39902290442518784 |
"Site A" |
0.16890325301726694 |
"About" |
0.11220151747374331 |
"Links" |
0.11220151747374331 |
"Product" |
0.11220151747374331 |
"Site B" |
0.01890325301726691 |
"Site C" |
0.01890325301726691 |
"Site D" |
0.01890325301726691 |
Comparing these results to the ones from the stream example (which is not using sourceNodes
configuration parameter) shows that the 'Site A' node that we used in the sourceNodes
list now scores second instead of fourth.
Scaling centrality scores
To normalize the final scores as part of the algorithm execution, one can use the scaler
configuration parameter.
A description of all available scalers can be found in the documentation for the scaleProperties
procedure.
stream
mode and returns normalized results:CALL gds.pageRank.stream('myGraph', {
scaler: "MEAN"
})
YIELD nodeId, score
RETURN gds.util.asNode(nodeId).name AS name, score
ORDER BY score DESC, name ASC
name | score |
---|---|
"Home" |
0.780671346390832 |
"About" |
0.032214422681946 |
"Links" |
0.032214422681946 |
"Product" |
0.032214422681946 |
"Site A" |
-0.219328653609168 |
"Site B" |
-0.219328653609168 |
"Site C" |
-0.219328653609168 |
"Site D" |
-0.219328653609168 |
Comparing the results with the stream example, we can see that the relative order of scores is the same.