北风推荐引擎

最近，我被要求提出一种提供推荐的方法。幸运的是，通过在最近的Neo4j伦敦聚会上从Max De Marzi和Mark Needham的演讲中获得的知识，我知道这可以很容易地通过Neo4j实现。

推荐引擎的关键问题在于数据。幸运的是，Neo4j捆绑了Northwind图示例。Northwind数据库是一个著名的包含购买历史的数据集，多年来一直用于教授关系数据库，是开始的好地方。

您可以通过遵循Neo4j上“将数据导入Neo4j”的帖子，将Northwind数据库导入图谱中，或者在Neo4j的浏览器中输入以下内容，例如Neo4j Desktop中的空数据库或空白沙盒。

:play northwind graph

以下是手动加载数据的方法

添加索引、约束并加载数据

CREATE INDEX ON :Product(productID);
CREATE INDEX ON :Product(productName);
CREATE INDEX ON :Category(categoryID);
CREATE INDEX ON :Employee(employeeID);
CREATE INDEX ON :Supplier(supplierID);
CREATE INDEX ON :Customer(customerID);
CREATE INDEX ON :Customer(customerName);
CREATE CONSTRAINT ON (o:Order) ASSERT o.orderID IS UNIQUE;

// Create customers
 USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/customers.csv" AS row
CREATE (:Customer {companyName: row.companyName, customerID: row.customerID, fax: row.fax, phone: row.phone});

// Create products
USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/products.csv" AS row
CREATE (:Product {productName: row.productName, productID: row.productID, unitPrice: toFloat(row.UnitPrice)});

// Create suppliers
USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/suppliers.csv" AS row
CREATE (:Supplier {companyName: row.companyName, supplierID: row.supplierID});

// Create employees
USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/employees.csv" AS row
CREATE (:Employee {employeeID:row.employeeID,  firstName: row.firstName, lastName: row.lastName, title: row.title});

// Create categories
USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/categories.csv" AS row
CREATE (:Category {categoryID: row.categoryID, categoryName: row.categoryName, description: row.description});

// Create Orders
 USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/orders.csv" AS row
MERGE (o:Order {orderID: row.orderID}) ON CREATE SET o.shipName =  row.shipName;

// Relate orders to products
 USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/order-details.csv" AS row
MATCH (o:Order {orderID: row.orderID})
MATCH (product:Product {productID: row.productID})
MERGE (o)-[pu:PRODUCT]->(product)
ON CREATE SET pu.unitPrice = toFloat(row.unitPrice), pu.quantity = toFloat(row.quantity);

// Relate Orders to Employees
 USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/orders.csv" AS row
MATCH (o:Order {orderID: row.orderID})
MATCH (employee:Employee {employeeID: row.employeeID})
MERGE (employee)-[:SOLD]->(o);

// Relate customers to orders
 USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/orders.csv" AS row
MATCH (o:Order {orderID: row.orderID})
MATCH (customer:Customer {customerID: row.customerID})
MERGE (customer)-[:PURCHASED]->(o);

// Relate Products to suppliers
 USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/products.csv" AS row
MATCH (product:Product {productID: row.productID})
MATCH (supplier:Supplier {supplierID: row.supplierID})
MERGE (supplier)-[:SUPPLIES]->(product);

// Relate Products to Categories
 USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/products.csv" AS row
MATCH (product:Product {productID: row.productID})
MATCH (category:Category {categoryID: row.categoryID})
MERGE (product)-[:PART_OF]->(category);

// Relate employees to managers
 USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/employees.csv" AS row
MATCH (employee:Employee {employeeID: row.employeeID})
MATCH (manager:Employee {employeeID: row.reportsTo})
MERGE (employee)-[:REPORTS_TO]->(manager);

// Add unit price
 USING PERIODIC COMMIT 100
LOAD CSV WITH HEADERS FROM "https://raw.githubusercontent.com/adam-cowley/northwind-neo4j/master/data/order-details.csv" AS row
MATCH (o:Order {orderID: row.orderID})
MATCH (product:Product {productID: row.productID})
MERGE (o)-[pu:PRODUCT]->(product)
ON CREATE SET pu.unitPrice = toFloat(row.unitPrice), pu.quantity = toFloat(row.quantity);

现在我们有了一些数据，让我们开始探索这个数据集。

数据集

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Northwind图为我们提供了丰富的数据集，但我们主要关注客户及其订单。在图中，数据建模如下

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基于内容的推荐

我们能为客户做出的最简单的推荐是基于内容的推荐。根据他们之前的购买记录，我们能否向他们推荐任何他们尚未购买的商品？对于我们的客户购买的每件产品，让我们看看其他客户还购买了什么。每个:Product都与一个:Category相关联，因此我们可以用它来进一步缩小推荐产品列表。

match (c:Customer)-[:PURCHASED]->(o:Order)-[:PRODUCT]->(p:Product)
<-[:PRODUCT]-(o2:Order)-[:PRODUCT]->(p2:Product)-[:PART_OF]->(:Category)<-[:PART_OF]-(p)
WHERE c.customerID = 'ANTON' and NOT( (c)-[:PURCHASED]->(:Order)-[:PRODUCT]->(p2) )
return c.companyName, p.productName as has_purchased, p2.productName as has_also_purchased, count(DISTINCT o2) as occurrences
order by occurrences desc
limit 5

目前为止相当标准。

协同过滤

协同过滤是推荐引擎使用的一种技术，它根据其他客户的反馈来推荐内容。为此，我们可以使用k-NN（k最近邻）算法。k-NN通过根据项目彼此之间的相似性将它们分组进行分类。在我们的案例中，这可能是两个客户对某个产品的评分。举一个现实世界的例子，Netflix等网站就是通过这种方式，根据你已经看过的节目的评分来提供推荐的。

要使这个模型起作用，我们首先需要创建一些“评分关系”。目前，让我们根据客户购买产品的次数，为每个产品创建一个介于0到1之间的分数。

MATCH (c:Customer)-[:PURCHASED]->(o:Order)-[:PRODUCT]->(p:Product)
WITH c, count(p) as total
MATCH (c)-[:PURCHASED]->(o:Order)-[:PRODUCT]->(p:Product)
WITH c, total,p, count(o)*1.0 as orders
MERGE (c)-[rated:RATED]->(p)
ON CREATE SET rated.rating = orders/total
ON MATCH SET rated.rating = orders/total
WITH c.companyName as company, p.productName as product, orders, total, rated.rating as rating
ORDER BY rating DESC
RETURN company, product, orders, total, rating LIMIT 10

现在我们的模型应该看起来像这样

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MATCH (me:Customer)-[r:RATED]->(p:Product)
WHERE me.customerID = 'ANTON'
RETURN p.productName, r.rating limit 10

现在我们可以使用这些评分来比较两位客户的偏好。

// See Customer's Similar Ratings to Others
MATCH (c1:Customer {customerID:'ANTON'})-[r1:RATED]->(p:Product)<-[r2:RATED]-(c2:Customer)
RETURN c1.customerID, c2.customerID, p.productName, r1.rating, r2.rating,
CASE WHEN r1.rating-r2.rating < 0 THEN -(r1.rating-r2.rating) ELSE r1.rating-r2.rating END as difference
ORDER BY difference ASC
LIMIT 15

现在，我们可以使用余弦相似度在两位客户之间创建相似性分数（感谢Nicole White提供的原始Cypher查询…）

MATCH (c1:Customer)-[r1:RATED]->(p:Product)<-[r2:RATED]-(c2:Customer)
WITH
	SUM(r1.rating*r2.rating) as dot_product,
	SQRT( REDUCE(x=0.0, a IN COLLECT(r1.rating) | x + a^2) ) as r1_length,
	SQRT( REDUCE(y=0.0, b IN COLLECT(r2.rating) | y + b^2) ) as r2_length,
	c1,c2
MERGE (c1)-[s:SIMILARITY]-(c2)
SET s.similarity = dot_product / (r1_length * r2_length)

MATCH (me:Customer)-[r:SIMILARITY]->(them)
WHERE me.customerID='ANTON'
RETURN me.companyName, them.companyName, r.similarity
ORDER BY r.similarity DESC limit 10

太棒了，现在让我们根据这些相似性分数进行推荐。

WITH 1 as neighbours
MATCH (me:Customer)-[:SIMILARITY]->(c:Customer)-[r:RATED]->(p:Product)
WHERE me.customerID = 'ANTON' and NOT ( (me)-[:RATED|PRODUCT|ORDER*1..2]->(p:Product) )
WITH p, COLLECT(r.rating)[0..neighbours] as ratings, collect(c.companyName)[0..neighbours] as customers
WITH p, customers, REDUCE(s=0,i in ratings | s+i) / LENGTH(ratings)  as recommendation
ORDER BY recommendation DESC
RETURN p.productName, customers, recommendation LIMIT 10

就是这样！使用Neo4j快速简单地实现推荐。

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GraphGists

北风推荐引擎

数据集

热门产品

基于内容的推荐

协同过滤