56
Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William Rand, and Michelle Girvan 31 October 2014

Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Page 1: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Predictively Optimal Communities in Dynamic Social Networks

David Darmon

in collaboration with

Erin Uhlfelder, William Rand, and Michelle Girvan31 October 2014

Page 2: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Dynamic Social Networks

▪ The networks are complicated.

Page 3: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Dynamic Social Networks

▪ The networks are complicated.

▪ The individual dynamics are complicated.

Page 4: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Dynamic Social Networks

▪ The networks are complicated.

▪ The individual dynamics are complicated.

▪ The interactions are complicated.

Page 5: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Dynamic Social Networks

Page 6: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Dynamic Social Networks

Page 7: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Dynamic Social Networks

Page 8: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Why Coarsen a Dynamic Network?

▪ Benefits of coarsening:■ Track the activity of collections of

users.

■ Track how collections of users respond to marketing, news events, etc.

■ Track how collections of users interact.

Page 9: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Standard Approachesto Network Coarsening

Page 10: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Coarsen by Structure

▪ Many standard methods coarsen a network based on structural properties of the network.

▪ Ex: Community detection-based methods determine collections of users that are more densely connected inside than outside of a community.

Page 11: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Coarsen by Dynamic Dyadic Relationships

▪ Determine pairwise statistics based on observed dynamics to quantify the interaction between users:

■ Correlation■ Granger causality■ Transfer entropy

▪ Use these statistics to construct a weighted network, and infer communities using theweighted network.

Page 12: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Drawbacks of Standard Approaches

▪ In dynamic social networks, many ‘edges’ are spurious.■ Ex: A single user may follow thousands of

other users, but only interact with a subset of them.

▪ Pairwise dynamical relationships may be very weak.

Page 13: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Coarsen by Predictive Partitioning

▪ Take advantage of both:■ the structure of the network■ the dynamics occurring on the network

to define partitions of the network based on mesoscopic dynamics.

▪ Define these partitions to result in mesoscale view of the network that is predictively optimal.

Page 14: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Sketch ofPredictive Partitioning

Page 15: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William
Page 16: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Page 17: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William
Page 18: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William
Page 19: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Page 20: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William
Page 21: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Page 22: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Page 23: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Formulation ofPredictive Partitioning

Page 24: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Formulation of Predictive Partitioning — Node Dynamics

▪ Consider a network of N nodes.

▪ Let denote the observed activity of node u at time t.

Xu(t)

Xu(t)

Xv(t)

Page 25: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Formulation of Predictive Partitioning — Network Partition

▪ Consider a partition CC of the nodes into G disjoint communities:

C = {C1, C2, . . . , CG}

C1

C2

C3C4

Page 26: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Formulation of Predictive Partitioning — Community Dynamics

▪ For a community c, define the aggregated activity at time t:

C1C2

C3C4

Ac(t) =X

u2Cc

Xu(t)

= Aggregated activity of nodes in Cc

A2(t)

A4(t)

A1(t)

A3(t)

Page 27: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Formulation of Predictive Partitioning — Normalization

▪ Let the normalized activity of community c be

A2(t)

A4(t)

C1C2

C3C4

A3(t)

A1(t)

Ac(t) =Ac(t)� sc(t)

�c(t)

=Observed Activity� Seasonal Activity

Seasonal Variability

Page 28: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Formulation of Predictive Partitioning — Predictability

▪ The predictability of the normalized activities are what we wish to optimize by an

appropriate choice of CC.{{Ac(t)}}Cc=1

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A3(t)

A1(t)

Page 29: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Formulation of Predictive Partitioning — Predictability

▪ As a predictability metric, use the redundancy of the normalized activity,

where:

■ is the marginal differential entropy

■ is the differential entropy rate

R⇣Ac

⌘= h

norm

⇣Ac

⌘� h

⇣Ac

hnorm

⇣Ac

h⇣Ac

Page 30: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Formulation of Predictive Partitioning — Predictability

▪ The marginal differential entropy measures how unpredictable the normalized activity is when viewed as Gaussian white noise, ignoring any memory:

▪ The differential entropy rate measures how unpredictable the normalized activity is once we have accounted for any memory in the activity:

h⇣Ac

⌘= h

✓Ac(t)

����Ac(t� 1), Ac(t� 2), . . .

hnorm

⇣Ac

Page 31: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Formulation of Predictive Partitioning — Predictability

▪ Thus, the redundancy measures how much more predictable the activity is compared to white noise.

R⇣Ac

⌘= h

norm

⇣Ac

⌘� h

⇣Ac

Page 32: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Formulation of Predictive Partitioning — Predictability

▪ For the partition CC, define the overall redundancy of its induced dynamics by

R(C) =X

c

R⇣Ac

⌘.

Page 33: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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A~c(t)

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R(C) > R(C0)

C C0

Page 34: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Demonstration withSynthetic Data

Page 35: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Synthetic Data — Network

▪ Directed Erdös-Rényi network withN = 160 nodesp = 0.05 connection probability

User j

Use

r i

Page 36: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

1

2

3

4

◆2!1

◆1!4◆1!3

◆3!4

Page 37: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

1

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◆1!4◆1!3

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Synthetic Data — Dynamics

▪ Bass-like Poissonian dynamics:

▪ i.e. The expected activity of user u at time t is their background rate plus the influence from their inputs.

Xu(t)|X(t� 1) ⇠ Poisson(�u(t))

where

r(t) =A

2(sin(!t) + 1)

r(t)

�u(t) = r(t) +X

v2Pa(u)

◆v!uXv(t� 1).

Page 38: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

1

2

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4

◆2!1

◆1!4◆1!3

◆3!4

Synthetic Data — Dynamics

▪ Example:

where

X3(t)|X(t� 1) = X3(t)|{X1(t� 1)}⇠ Poisson(�3(t))

�3(t) = r(t) + ◆1!3X1(t� 1).

Page 39: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

1

2

3

4

◆2!1

◆1!4◆1!3

◆3!4

Synthetic Data — Dynamical Communities

▪ Assume 4 dynamical communities, each of 40 users.

▪ Set influence inside of a dynamical community to be ten times the influence outside of a dynamical community:

◆inside

= 10⇥ ◆outside

.

Page 40: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Page 41: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Synthetic Data — Experiment

▪ Partition the network into

2, 4, 10, 16, 20, 32, 40

communities.

▪ Use both non-randomized and randomized partitions.

Page 42: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

▪ Example: 40 communities of size 4.

Synthetic Data — Experiment

...

...

Dynamical Community 1

Dynamical Community 2

Dynamical Community 3

Dynamical Community 4

Non-randomized:

Randomized:

Page 43: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Synthetic Data — Results

●●

●● ●●

●●

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1.0

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1.4

Number of Communities

Tota

l Red

unda

ncy

●●

2 4 10 16 20 32 40

Non-randomizedPartition

Randomized Partition

Page 44: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Demonstration withData from Twitter

Page 45: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Twitter Data — The Dataset

▪ Network: 15K network of Twitter users collected via a breadth first search of followers / friends.

▪ Dynamics: Individual statuses collected over7-week period in Summer 2014.

Page 46: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Page 47: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Twitter Data — Comparison of Community Partitions

▪ Use the partitions inferred by popular community detection algorithms:

■ Fast-Greedy Algorithm for Modularity Maximization■ Louvain Algorithm for Modularity Maximization■ Newman’s Spectral Method

Method Total Redundancy

Fast-Greedy 0.671

Louvain 1.050

Spectral 0.793

Total Network 0.203

Page 48: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Conclusions

Page 49: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Conclusions

▪ The networks are complicated.

▪ The individual dynamics are complicated.

▪ The interactions are complicated.

Page 50: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Conclusions

▪ By taking advantage of both:■ the structure of the network■ the dynamics occurring on the network

we can define partitions of the network based on its mesoscopic dynamics.

▪ By optimizing the predictability of the mesoscopic dynamics, we can detect communities ‘hidden’ from more standard community detection algorithms.

Page 51: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Thank you.

[email protected]

Page 52: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

Future Work

▪ Formulate an optimization problem to find predictively optimal communities.

▪ Possible approaches:■ Greedy optimization based on merging of

communities.■ Take advantage of multilevel representations of

structural communities to determine the ‘right’ level from a predictive viewpoint.

Page 53: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Page 54: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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Page 55: Predictively Optimal Communities in Dynamic Social Networks · Predictively Optimal Communities in Dynamic Social Networks David Darmon in collaboration with Erin Uhlfelder, William

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