How to Load and Build Networks

Goal: Create multilayer networks from scratch or load them from files.

Prerequisites: Basic Python knowledge. For conceptual background, see The py3plex Core Model.

Creating Networks from Scratch

Method 1: Add Edges Directly (Recommended)

The simplest approach—nodes are created automatically when you add edges.

from py3plex.core import multinet

# Create empty network
network = multinet.multi_layer_network()

# Add edges in list format
# Format: [source_node, source_layer, target_node, target_layer, weight]
network.add_edges([
    ['Alice', 'friends', 'Bob', 'friends', 1.0],
    ['Bob', 'friends', 'Carol', 'friends', 1.0],
    ['Alice', 'colleagues', 'Bob', 'colleagues', 1.0],
    ['Bob', 'colleagues', 'Dave', 'colleagues', 1.0]
], input_type="list")

# Verify
stats = network.basic_stats()

Expected output:

Number of nodes: 6
Number of edges: 4
Number of unique node IDs (across all layers): 4
Nodes per layer:
  Layer 'friends': 3 nodes
  Layer 'colleagues': 3 nodes

Method 2: Add Nodes First

For more control over node attributes:

from py3plex.core import multinet

network = multinet.multi_layer_network()

# Add nodes explicitly (as node-layer tuples)
network.add_nodes([
    ('Alice', 'friends'),
    ('Bob', 'friends'),
    ('Carol', 'friends'),
    ('Alice', 'colleagues'),
    ('Bob', 'colleagues'),
    ('Dave', 'colleagues')
])

# Add edges between existing nodes
network.add_edges([
    [('Alice', 'friends'), ('Bob', 'friends'), 1.0],
    [('Bob', 'friends'), ('Carol', 'friends'), 1.0]
])

Method 3: Use Dictionary Format

For networks with edge attributes:

network = multinet.multi_layer_network()

# Add edges with custom attributes
network.add_edges([
    {
        'source': 'Alice',
        'source_type': 'friends',
        'target': 'Bob',
        'target_type': 'friends',
        'weight': 1.0,
        'timestamp': '2024-01-15',
        'interaction_type': 'message'
    },
    {
        'source': 'Bob',
        'source_type': 'friends',
        'target': 'Carol',
        'target_type': 'friends',
        'weight': 2.5,
        'timestamp': '2024-01-16'
    }
], input_type="dict")

Loading Networks from Files

Load Edge Lists

Most common format: one edge per line.

File format (stored as datasets/simple_multiplex.txt in the repository):

Alice friends Bob friends 1.0
Bob friends Carol friends 1.0
Alice colleagues Bob colleagues 1.0

Load it:

from py3plex.core import multinet

network = multinet.multi_layer_network()

# Option 1: Load from repository file
network.load_network(
    "datasets/simple_multiplex.txt",
    input_type="multiedgelist"
)

# Option 2: Create from data directly (recommended for examples)
network.add_edges([
    ['Alice', 'friends', 'Bob', 'friends', 1.0],
    ['Bob', 'friends', 'Carol', 'friends', 1.0],
    ['Alice', 'colleagues', 'Bob', 'colleagues', 1.0],
], input_type="list")

network.basic_stats()

Load from Pandas DataFrame

Convert tabular data to networks:

import pandas as pd
from py3plex.core import multinet

# Your data
df = pd.DataFrame({
    'source': ['Alice', 'Bob', 'Alice'],
    'layer': ['friends', 'friends', 'work'],
    'target': ['Bob', 'Carol', 'Carol'],
    'weight': [1.0, 1.0, 2.0]
})

# Convert to network
network = multinet.multi_layer_network()

for _, row in df.iterrows():
    network.add_edge(
        row['source'], row['layer'],
        row['target'], row['layer'],
        weight=row['weight']
    )

Load from JSON

For complex networks with metadata:

import json
from py3plex.core import multinet

# Load JSON
with open('network.json', 'r') as f:
    data = json.load(f)

network = multinet.multi_layer_network()

# Assuming JSON structure: {"edges": [...], "nodes": [...]}
for edge in data['edges']:
    network.add_edge(
        edge['source'], edge['source_layer'],
        edge['target'], edge['target_layer'],
        **edge.get('attributes', {})
    )

Load from NetworkX

Convert existing single-layer networks:

import networkx as nx
from py3plex.core import multinet

# Existing NetworkX graph
G = nx.karate_club_graph()

# Convert to multilayer (single layer)
network = multinet.multi_layer_network()

for u, v in G.edges():
    network.add_edge(u, 'layer1', v, 'layer1')

Loading with Inter-layer Edges

To represent the same entity across layers:

network = multinet.multi_layer_network()

# Intra-layer edges
network.add_edges([
    ['Alice', 'friends', 'Bob', 'friends', 1.0],
    ['Alice', 'work', 'Carol', 'work', 1.0],
], input_type="list")

# Inter-layer edges (same person across layers)
network.add_edge('Alice', 'friends', 'Alice', 'work', type='interlayer')
network.add_edge('Bob', 'friends', 'Bob', 'work', type='interlayer')

Common Patterns

Pattern 2: Heterogeneous Networks

Different entity types:

# Author-Paper bipartite network
network = multinet.multi_layer_network()
network.add_edges([
    ['Alice', 'authors', 'Paper1', 'papers', 1],
    ['Bob', 'authors', 'Paper1', 'papers', 1],
    ['Alice', 'authors', 'Paper2', 'papers', 1],
], input_type="list")

Pattern 3: Temporal Networks

Time-stamped edges:

network = multinet.multi_layer_network()
network.add_edges([
    {
        'source': 'Alice',
        'source_type': 'social',
        'target': 'Bob',
        'target_type': 'social',
        't': '2024-01-15T10:00:00'  # Point in time
    },
    {
        'source': 'Bob',
        'source_type': 'social',
        'target': 'Carol',
        'target_type': 'social',
        't_start': '2024-01-15',     # Time range
        't_end': '2024-01-20'
    }
], input_type="dict")

See API Documentation for temporal network details.

Verifying Your Network

After loading, verify the structure:

# Basic stats
network.basic_stats()

# Get specific information
layers = network.get_layers()
print(f"Layers: {layers}")

num_nodes = len(list(network.get_nodes()))
print(f"Total nodes: {num_nodes}")

# Check a specific layer
from py3plex.dsl import Q, L
layer_nodes = Q.nodes().from_layers(L["friends"]).execute(network)
print(f"Friends layer: {len(layer_nodes)} nodes")