Introduction to graph theory

Basically, a graph is a data structure that's able to represent relations in a collection of objects. Under this paradigm, the objects are the graph's nodes and the relations are the graph's links (or edges). The graph is directed if the links have an orientation (conceptually, they're like the one-way streets of a city); otherwise, the graph is undirected. In the following table, examples of well-known graphs are provided:

Graph example

Type

Nodes

Edges

World Wide Web

Directed

Web pages

Links

Facebook

Undirected

People

Friendship

Twitter

Directed

People

Follower

IP network

Undirected

Hosts

Wires/Connections

Navigation systems

Directed

Places/Addresses ...

Get Python Data Science Essentials - Third Edition now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.