BERTopic

BERTopic is a topic modeling technique that leverages 🤗 transformers and c-TF-IDF to create dense clusters allowing for easily interpretable topics whilst keeping important words in the topic descriptions.

BERTopic supports guided, (semi-) supervised, and dynamic topic modeling. It even supports visualizations similar to LDAvis!

Corresponding medium posts can be found here and here.

Installation

Installation, with sentence-transformers, can be done using pypi:

pip install bertopic

You may want to install more depending on the transformers and language backends that you will be using. The possible installations are:

pip install bertopic[flair]
pip install bertopic[gensim]
pip install bertopic[spacy]
pip install bertopic[use]

Getting Started

For an in-depth overview of the features of BERTopic you can check the full documentation here or you can follow along with one of the examples below:

Name	Link
Topic Modeling with BERTopic
(Custom) Embedding Models in BERTopic
Advanced Customization in BERTopic
(semi-)Supervised Topic Modeling with BERTopic
Dynamic Topic Modeling with Trump's Tweets
Topic Modeling arXiv Abstracts

Quick Start

We start by extracting topics from the well-known 20 newsgroups dataset which is comprised of english documents:

from bertopic import BERTopic
from sklearn.datasets import fetch_20newsgroups
 
docs = fetch_20newsgroups(subset='all',  remove=('headers', 'footers', 'quotes'))['data']

topic_model = BERTopic()
topics, probs = topic_model.fit_transform(docs)

After generating topics, we can access the frequent topics that were generated:

>>> topic_model.get_topic_info()

Topic	Count	Name
-1	4630	-1_can_your_will_any
0	693	49_windows_drive_dos_file
1	466	32_jesus_bible_christian_faith
2	441	2_space_launch_orbit_lunar
3	381	22_key_encryption_keys_encrypted

-1 refers to all outliers and should typically be ignored. Next, let's take a look at the most frequent topic that was generated, topic 0:

>>> topic_model.get_topic(0)

[('windows', 0.006152228076250982),
 ('drive', 0.004982897610645755),
 ('dos', 0.004845038866360651),
 ('file', 0.004140142872194834),
 ('disk', 0.004131678774810884),
 ('mac', 0.003624848635985097),
 ('memory', 0.0034840976976789903),
 ('software', 0.0034415334250699077),
 ('email', 0.0034239554442333257),
 ('pc', 0.003047105930670237)]

NOTE: Use BERTopic(language="multilingual") to select a model that supports 50+ languages.

Visualize Topics

After having trained our BERTopic model, we can iteratively go through hundreds of topics to get a good understanding of the topics that were extracted. However, that takes quite some time and lacks a global representation. Instead, we can visualize the topics that were generated in a way very similar to LDAvis:

topic_model.visualize_topics()

We can create an overview of the most frequent topics in a way that they are easily interpretable. Horizontal barcharts typically convey information rather well and allow for an intuitive representation of the topics:

topic_model.visualize_barchart()

Find all possible visualizations with interactive examples in the documentation here.

Embedding Models

BERTopic supports many embedding models that can be used to embed the documents and words:

• Sentence-Transformers
• Flair
• Spacy
• Gensim
• USE

Sentence-Transformers is typically used as it has shown great results embedding documents meant for semantic similarity. Simply select any from their documentation here and pass it to BERTopic:

topic_model = BERTopic(embedding_model="all-MiniLM-L6-v2")

Flair allows you to choose almost any 🤗 transformers model. Simply select any from here and pass it to BERTopic:

from flair.embeddings import TransformerDocumentEmbeddings

roberta = TransformerDocumentEmbeddings('roberta-base')
topic_model = BERTopic(embedding_model=roberta)

Click here for a full overview of all supported embedding models.

Dynamic Topic Modeling

Dynamic topic modeling (DTM) is a collection of techniques aimed at analyzing the evolution of topics over time. These methods allow you to understand how a topic is represented over time. Here, we will be using all of Donald Trump's tweet to see how he talked over certain topics over time:

import re
import pandas as pd

trump = pd.read_csv('https://drive.google.com/uc?export=download&id=1xRKHaP-QwACMydlDnyFPEaFdtskJuBa6')
trump.text = trump.apply(lambda row: re.sub(r"http\S+", "", row.text).lower(), 1)
trump.text = trump.apply(lambda row: " ".join(filter(lambda x:x[0]!="@", row.text.split())), 1)
trump.text = trump.apply(lambda row: " ".join(re.sub("[^a-zA-Z]+", " ", row.text).split()), 1)
trump = trump.loc[(trump.isRetweet == "f") & (trump.text != ""), :]
timestamps = trump.date.to_list()
tweets = trump.text.to_list()

Then, we need to extract the global topic representations by simply creating and training a BERTopic model:

topic_model = BERTopic(verbose=True)
topics, probs = topic_model.fit_transform(tweets)

From these topics, we are going to generate the topic representations at each timestamp for each topic. We do this by simply calling topics_over_time and pass in his tweets, the corresponding timestamps, and the related topics:

topics_over_time = topic_model.topics_over_time(tweets, topics, timestamps, nr_bins=20)

Finally, we can visualize the topics by simply calling visualize_topics_over_time():

topic_model.visualize_topics_over_time(topics_over_time, top_n_topics=6)

Overview

For quick access to common functions, here is an overview of BERTopic's main methods:

Method	Code
Fit the model	.fit(docs)
Fit the model and predict documents	.fit_transform(docs)
Predict new documents	.transform([new_doc])
Access single topic	.get_topic(topic=12)
Access all topics	.get_topics()
Get topic freq	.get_topic_freq()
Get all topic information	.get_topic_info()
Get representative docs per topic	.get_representative_docs()
Get topics per class	.topics_per_class(docs, topics, classes)
Dynamic Topic Modeling	.topics_over_time(docs, topics, timestamps)
Update topic representation	.update_topics(docs, topics, n_gram_range=(1, 3))
Reduce nr of topics	.reduce_topics(docs, topics, nr_topics=30)
Find topics	.find_topics("vehicle")
Save model	.save("my_model")
Load model	BERTopic.load("my_model")
Get parameters	.get_params()

For an overview of BERTopic's visualization methods:

Method	Code
Visualize Topics	.visualize_topics()
Visualize Topic Hierarchy	.visualize_hierarchy()
Visualize Topic Terms	.visualize_barchart()
Visualize Topic Similarity	.visualize_heatmap()
Visualize Term Score Decline	.visualize_term_rank()
Visualize Topic Probability Distribution	.visualize_distribution(probs[0])
Visualize Topics over Time	.visualize_topics_over_time(topics_over_time)
Visualize Topics per Class	.visualize_topics_per_class(topics_per_class)

Citation

To cite BERTopic in your work, please use the following bibtex reference:

@misc{grootendorst2020bertopic,
  author       = {Maarten Grootendorst},
  title        = {BERTopic: Leveraging BERT and c-TF-IDF to create easily interpretable topics.},
  year         = 2020,
  publisher    = {Zenodo},
  version      = {v0.9.2},
  doi          = {10.5281/zenodo.4381785},
  url          = {https://doi.org/10.5281/zenodo.4381785}
}