Point-of-Interest Recommendations: Learning Potential Check-ins from Friends

1

Huayu Li∗, Yong Ge+, Richang Hong−, Hengshu Zhu×

∗University of North Carolina at Charlotte

+University of Arizona

−Hefei University of Technology×

Baidu Research-Big Data Lab

Outline

Introduction

Research Problem

Research Challenges

Related Work

Methodologies

Experiments

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Introduction

3

Users Mobile DevicesLocation-based Social

Network (LBSN) Services

4

Introduction

5

Introduction

6

Introduction

7

Introduction

Information Overload• Foursquare: 65 million venues

• Facebook: 16 million local business

• Yelp: 2.1 million claimed business

New Region

Which One?

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Introduction

Information Overload• Foursquare: 65 million venues

• Facebook: 16 million local business

• Yelp: 2.1 million claimed business

New Region

Which One? A location recommender system is very important!

Research Problem

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Given a set of users and a set of locations they have visited

before, the objective is to recommend the locations to an

individual who might have interest to visit.

visited recommended

Research Challenges

Complex Decision Making Process• Social Network Influence

• Geographical Influence

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Research Challenges

Complex Decision Making Process• Social Network Influence

• Geographical Influence

Data Sparsity Issue• Each user only visits a limited number of locations.

• For new user/location, we do not have their check-in information.

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Research Challenges

Complex Decision Making Process• Social Network Influence

• Geographical Influence

Data Sparsity Issue• Each user only visits a limited number of locations.

• For new user/location, we do not have their check-in information.

Implicit Feedback Issue• Only check-in frequency without explicit rating.

• We do not know user’s explicit preference for locations.

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Related Work

Modeling Social Network Influence• Social regularization constraint (WSDM’11)

• Social correlations (CIKM’12, IJCAI’13, ICDM’15)

• User-based collaborative filtering (SIGIR’11)

Modeling geographical influence• Incorporating geographical distance (KDD’11, SIGIR’11, AAAI’12,

SIGSPATIAL’ 13, KDD’14, ICDM’15)

• Incorporating activity area (KDD’ 14)

• Incorporation nearest neighbors (CIKM’14)

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Methods: Framework

Learn potential locations from

friends

Learn user’s preference for

locations

14

Methods: Framework

Learn potential locations from

friends

Learn user’s preference for

locations

15

Definition of Friends

Social Friends ℱ𝑖s

• The users who socially connect with the target user 𝑖 in LBSNs.

Location Friends ℱ𝑖𝑙

• The users who check-in the same locations as the target user 𝑖.

Neighboring Friends ℱ𝑖𝑛

• The users who live physically closest to the target user 𝑖.

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𝑙1𝑙2

𝑙3𝑙4 𝑙5

𝑓1

𝑓2

𝑓3

𝑓4

𝑓5

𝑓6

𝑢𝑖

Definition of Friends

Social Friends ℱ𝑖s

• The users who socially connect with the target user 𝑖 in LBSNs.

Location Friends ℱ𝑖𝑙

• The users who check-in the same locations as the target user 𝑖.

Neighboring Friends ℱ𝑖𝑛

• The users who live physically closest to the target user 𝑖.

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𝑙1𝑙2

𝑙3𝑙4 𝑙5

𝑓1

𝑓2

𝑓3

𝑓4

𝑓5

𝑓6

𝑢𝑖

ℱi = ℱ𝑖s ∪ 𝑆(ℱ𝑖

𝑙) ∪ 𝑆(ℱ𝑖𝑛)

Methods: Learning Potential Locations

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𝑢𝑖PROBLEM DEFINITION:For the target user 𝑖, given

a set of locations that her

friends have checked-in

before but she never visits,

the problem is to find top

most potential locations that

she might be interested in.

Methods: Learning Potential Locations

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𝑢𝑖

𝑃𝑖𝑗𝑝𝑜𝑡

?

𝑙𝑗

Location Candidate

Linear Aggregation

Random Walk

Methods: Linear Aggregation

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𝑢𝑖

𝑙𝑗

Probability 𝑃𝑖𝑗𝑝𝑜𝑡

that

user 𝑖 visits a location 𝑗:

𝑃𝑖𝑗𝑝𝑜𝑡

∝ max𝑓∈ℱ

𝑖𝑗{𝑆𝑖𝑚(𝑖, 𝑓; 𝑗)}

𝜁𝑆𝑖𝑚𝑢 𝑖, 𝑓 + (1 − 𝜁)𝑃𝑖𝑗𝐺

Similarity of User Interest Similarity of Geo-location

Methods: Random Walk

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𝑢𝑖 Nodes: users and locations

Links: user-user, user-location, location-location

𝐲 = 1 − 𝛽 𝐀𝐲 +𝛽

|ℳ𝑖𝑜∩ℳ𝑖

𝑓|+|ℱ𝑖|+1

x

𝑃𝑖𝑗𝑝𝑜𝑡

is the steady probability

corresponding to location j

Transition Matrix Restart Nodes

Methods: Learning Potential Locations

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Observed Locations Potential Locations Other Unobserved Locations

Methods: Framework

Learn potential locations from

friends

Learn user’s preference for

locations

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Recommendation Models

The preference Ƹ𝑝𝑖𝑗 of user 𝑖 for location 𝑗:

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≈×d

⊙Users’ preference for locations

Category FeatureMatrix

Location Latent Matrix

User Latent Matrix

Ƹ𝑝𝑖𝑗 = (𝑞𝑖𝑐𝑗 + 𝜀) 𝐮𝑖𝑇𝐯𝑗

User’s Preference for Category

Tuning Parameter

User’s Typical Preference for Location

𝐏 ෩𝐐 = 𝐐 + 𝛆

𝐔

𝐕

Recommendation Models

Loss function of general form

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argmin𝐔,𝐕,𝐐

𝑖

𝐸𝑖 𝑝𝑖𝑗 , 𝑝𝑖𝑘 , 𝑝𝑖ℎ , ො𝑝𝑖𝑗 , ො𝑝𝑖𝑘 , ො𝑝𝑖ℎ + Θ(𝐔, 𝐕,𝐐)

∀ 𝑗 ∈ ℳ𝑖𝑜, 𝑘 ∈ ℳ𝑖

𝑝, ℎ ∈ ℳ𝑖

𝑢

Estimated Value

Observed Locations

Potential Locations

Other Unobserved Locations

Recommendation Models

Loss function of general form

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argmin𝐔,𝐕,𝐐

𝑖

𝐸𝑖 𝑝𝑖𝑗 , 𝑝𝑖𝑘 , 𝑝𝑖ℎ , ො𝑝𝑖𝑗 , ො𝑝𝑖𝑘 , ො𝑝𝑖ℎ + Θ(𝐔, 𝐕,𝐐)

∀ 𝑗 ∈ ℳ𝑖𝑜, 𝑘 ∈ ℳ𝑖

𝑝, ℎ ∈ ℳ𝑖

𝑢

Estimated Value

Observed Locations

Potential Locations

Other Unobserved Locations

𝜆𝑢

2||𝐔||2

2 +𝜆𝑣

2||𝐕||2

2+𝜆𝑞

2||𝐐||2

2

Regularization Term

Recommendation Models

Loss function of general form

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argmin𝐔,𝐕,𝐐

𝑖

𝐸𝑖 𝑝𝑖𝑗 , 𝑝𝑖𝑘 , 𝑝𝑖ℎ , ො𝑝𝑖𝑗 , ො𝑝𝑖𝑘 , ො𝑝𝑖ℎ + Θ(𝐔, 𝐕,𝐐)

∀ 𝑗 ∈ ℳ𝑖𝑜, 𝑘 ∈ ℳ𝑖

𝑝, ℎ ∈ ℳ𝑖

𝑢

Observed Locations

Potential Locations

Other Unobserved Locations

𝜆𝑢

2||𝐔||2

2 +𝜆𝑣

2||𝐕||2

2+𝜆𝑞

2||𝐐||2

2

Regularization Term

Square Error based Model Ranking Error based Model

Square Error based Model

The user’s preference for a location is defined as:

𝑝𝑖𝑗 = ൞

1 𝑖𝑓 𝑗 ∈ ℳio

𝛼 𝑖𝑓 𝑗 ∈ ℳi𝑝

0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒

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Observed Locations

Potential Locations

Other unobserved Locations

Square Error based Model

The user’s preference for a location is defined as:

𝑝𝑖𝑗 = ൞

1 𝑖𝑓 𝑗 ∈ ℳio

𝛼 𝑖𝑓 𝑗 ∈ ℳi𝑝

0 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒

Squared error loss function

𝐸𝑖 ∙ =

𝑗=1

𝑀

𝑤𝑖𝑗(𝑝𝑖𝑗 − Ƹ𝑝𝑖𝑗 )2

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𝑤𝑖𝑗 = ቊ1 + 𝛾 × 𝑟𝑖𝑗 , 𝑖𝑓 𝑗 ∈ ℳi

o

1, 𝑜𝑡ℎ𝑒𝑟𝑤𝑖𝑠𝑒

Weight Matrix

Square Error based Model

Squared error based objective function

ℒ

= min𝐔,𝐕,𝐐

𝑖=1

𝑁

𝑗=1

𝑀

𝑤𝑖𝑗(𝑝𝑖𝑗 − Ƹ𝑝𝑖𝑗 )2

+ Θ(𝐔, 𝐕, 𝐐)

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Initialization

Alternating Update

Alternating Least Square

Ranking Error based Model

Model the ranking order among user’s preference for three types of locations

ቊƸ𝑝𝑖𝑗 > Ƹ𝑝𝑖𝑘Ƹ𝑝𝑖𝑘 > Ƹ𝑝𝑖ℎ

, ∀ 𝑗 ∈ ℳ𝑖𝑜,𝑘 ∈ ℳ𝑖

𝑝, ℎ ∈ ℳ𝑖

𝑢

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Observed Location

Potential Location

Potential Location

Other Unobserved Location

Ranking Error based Model

Model the ranking order among user’s preference for three types of locations

ቊƸ𝑝𝑖𝑗 > Ƹ𝑝𝑖𝑘Ƹ𝑝𝑖𝑘 > Ƹ𝑝𝑖ℎ

, ∀ 𝑗 ∈ ℳ𝑖𝑜,𝑘 ∈ ℳ𝑖

𝑝, ℎ ∈ ℳ𝑖

𝑢

Ranking error loss function

𝐸𝑖 ∙ = −

𝑗∈ℳ𝑖𝑜

𝑘∈ℳ𝑖𝑝

ln 𝜎( Ƹ𝑝𝑖𝑗 − Ƹ𝑝𝑖𝑘) −

𝑘∈ℳ𝑖𝑝

ℎ∈ℳ𝑖𝑢

ln 𝜎( Ƹ𝑝𝑖𝑘 − Ƹ𝑝𝑖ℎ)

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Using Logistic Function to Model Ranking Order

Ranking Error based Model

Ranking error based objective function

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Initialization

Update

Stochastic Gradient Descent with Boostrap Sampling

Sampling

Incorporating Geographical Influence

Check-in probability is refined by a power-law function associated with the distance between user home position and a location.

Ƹ𝑝𝑖𝑗 ∝ 𝑝𝑖𝑗𝐺 × 𝜎( Ƹ𝑝𝑖𝑗)

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𝑝𝑜𝑤𝑒𝑟𝑙𝑎𝑤(𝑑(𝑖, 𝑗))

Recommendation Strategies

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Target User 𝑖

New Location

Standard Recommendation

New User RecommendationƸ𝑝𝑖𝑗 = (𝑞𝑖𝑐𝑗 + 𝜀) 𝐮𝑖

𝑇𝐯𝑗

New Location Recommendation

Ƹ𝑝𝑖𝑗 ∝ 𝑝𝑖𝑗𝐺× 𝜎

σ𝑙∈𝜓𝑗

𝑆𝑖𝑚𝐺(𝑗, 𝑙) Ƹ𝑝𝑖𝑙

σ𝑙∈𝜓𝑗

𝑆𝑖𝑚𝐺(𝑗, 𝑙)

Datasets: Gowalla

Test Methodology• Selecting 80% as training and using the rest 20% as testing according to

timestamp

Evaluation Metrics: • Top-K Recommendation Accuracy

(Precision@K and Recall@K)

Experiments

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Statistics of Data Set

New Location Rec New User Rec

#User #Location #Check-in Sparsity #New Location #Test #New User #Test

52,216 98,351 2,577,336 0.0399% 78,881 568,937 9,326 79,153

Exp. : Standard Recommendation

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Precision@K Recall@K

Modeling unobserved check-ins can improve recommendation accuracy !

Exp. : Standard Recommendation

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Precision@K Recall@K

Modeling potential check-ins can benefit recommendation!

Exp. : New User Recommendation

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Precision@K Recall@K

Modeling potential check-ins can solve user cold-start issue!

Exp. : New Location Recommendation

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Modeling potential check-ins can solve location cold-start issue!

Performance comparison for new location recommendation in terms of Precision@K and Recall@K.

Conclusion

Empirically analyze the correlations between users and their three type of friends using real-world data

Learn a set of locations for each user that her friends have checked-in before and she is most interested in

Develop matrix factorization based models via different error loss functions with the learned potential check-ins, and propose two scalable optimization methods

Design three different recommendation strategies

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Thank You